Phone system requirements checklist for open source PBX

Phone system requirements: how to use this checklist before choosing an open-source PBX

This checklist lists the requirements to settle before you pick an open-source PBX, explains how to verify each one, and identifies the answers that separate one build from another. Start with the questions that decide the shape of the system: how many users and sites you have, which of them need to be reached from outside, how many simultaneous calls each site must carry, and how your telephone numbers reach you through SIP trunks. Write the answers down as numbers and named sites, not as adjectives. "About 300 users across four offices" can be tested against a dial plan and a trunk sizing exercise. "Scalable" cannot. The checklist is organized by function, security, integration, operations and compliance. Under each heading, the requirement should be paired with a verification method: a test call, a document you can request from a vendor or partner, a configuration you can inspect, or a failover drill you can observe. A requirement without a verification method is an opinion, and opinions are hard to hold a partner to. For example, if you need survivability when the WAN fails, the verification is a scheduled test that disconnects a branch and records what still works. Ask the partner to describe that test before you sign.

Some items carry legal weight and need an earlier decision than the rest. Emergency calling, call recording and retention, and any voicemail or call content that may hold regulated data all shape the design, the logging and the evidence you will need later. Confirm with your counsel and compliance team which rules apply to your organization and which sites they cover, then ask each candidate partner how they would demonstrate those controls to an assessor. Keep in mind that a PBX configuration can be correct on the day it is built and wrong after the next change, so the verification plan should repeat after every significant change. Use the sibling pages on 911 compliance, RFP questions and cost to go deeper once this checklist is complete.

Which functional requirements decide the phone system build

This table lists the functional requirements that change how an Asterisk or FreePBX system is built, along with why each one matters and how to test it before committing. Read each row as a decision to settle in writing before selecting components. The main takeaway is that most build changes come from users, sites, trunks and porting, so verify those with test calls and a porting dry run early.

Requirement	Why it matters	How to verify it
Users and sites	Headcount, site count and remote staff set server sizing, redundancy design and which sites need local survivability.	Build a site inventory with user counts, concurrent call peaks and WAN links, then confirm the peak figures against call detail records from the current system.
Trunks and SIP providers	Trunk type, channel count and codec support determine capacity, failover paths and what the provider must support.	Request written channel and codec specifications from each provider, then run a test call matrix across inbound, outbound and failover trunks.
Number porting	Porting lead times and losses of service are often the longest dependency in a cutover plan.	Run a porting dry run with the losing carrier's paperwork, confirm the port order for each number range and check the exact loss-of-service rules with the provider.
Dial plan and extensions	The dial plan defines internal numbering, multi-site dialing and outbound rules that must match existing users' habits.	Export the current dial plan, map every pattern to its new equivalent, then test each pattern from every site with a scripted call matrix.
Queues and IVR	Queue strategy, overflow rules and IVR menus drive staffing, customer experience and any contact center add-ons.	Walk through each queue and menu with the business owner, then simulate peak and overflow scenarios with test agents and document the expected result for each.
Call recording	Recording scope, storage location and retention determine legal exposure and the records you must keep, search and produce.	Record a sample of calls across internal, external, queue and mobile legs, then check that each file plays back and that metadata matches the call.
Voicemail and after-hours routing	Voicemail storage, access controls and time-based routing decide where messages live and who can hear them when offices close.	Set a schedule with holiday and after-hours rules, then test each branch at boundary times and confirm voicemail notifications reach the right mailbox.
Softphones and desk phones	Endpoint mix sets provisioning effort, codec choices, network needs and which vendor firmware must be supported.	Pilot each endpoint model on the production network, including one home connection, and record call quality, registration stability and provisioning time.

Which security requirements apply to SIP trunks, softphones and call data

Telephony security problems usually start at the edges: SIP endpoints exposed to the internet, unencrypted signaling, and recordings or voicemail that nobody has scoped. The cards below cover the controls to settle before choosing an Asterisk or FreePBX design, and how to prove each one in a lab or pilot.

SIP exposure and registration controls

Every SIP trunk and softphone that reaches the public internet is a target for registration abuse and toll fraud. Decide which elements face the internet (trunk peers, remote registration, web-based softphones) and which stay on private networks. Require strong, unique credentials per endpoint, limits on registration attempts, and source address restrictions for trunks where the carrier publishes them. In a pilot, send failed registrations and unauthorized INVITE attempts from an outside host and confirm they are blocked and logged.

Encryption of signaling and media

Signaling and media are separate exposures. SIP signaling can run over TLS, and media can be encrypted with SRTP, but both depend on how the carrier, endpoints and PBX are configured. Confirm with your SIP trunk provider which transports and ciphers it supports, and whether it accepts encrypted media end to end. In the lab, capture traffic between a phone and the PBX and check that signaling and RTP payloads are not readable in clear text, and record any hop that is not encrypted as a documented exception.

Access to recordings and voicemail

Call recordings and voicemail files are stored data with their own access list. Define who can play, download, export or delete them, and separate supervisor access from administrator access. Check whether the storage location is encrypted at rest, whether access is tied to named accounts, and whether deletion follows the retention schedule. In a pilot, log in as a standard user, a supervisor and an administrator, then confirm each role can see only the recordings it should.

Administrative access and audit logging

Administrators can change dial plans, add trunks and turn on recording, so their actions need to be controlled and traceable. Require individual admin accounts, multi-factor authentication for the web interface where your platform supports it, and central logging of configuration changes and authentication events. Confirm the log retention period with your compliance lead. In a pilot, make a dial plan change under one admin account and verify that the change appears in the audit trail with a timestamp and user.

Protected health information in voicemail and recordings

Clinical and healthcare-adjacent teams may leave voicemail or record calls that contain protected health information. HIPAA's Security Rule addresses transmission security (45 CFR 164.312(e)(1)) and audit controls (164.312(b)), and a regulated buyer should be able to show how both apply to call data. Whether and how these rules apply to your organization is a question for counsel. Ask counsel to confirm applicability, then map which voicemail, recordings and call detail records are in scope, and verify in a pilot that transmission and access are logged and encrypted as documented.

Retention scope for regulated call recording

Broker-dealers face a specific preservation obligation: SEC Rule 17a-4(b)(4) requires preservation of communications relating to the business for not less than three years. Whether call recordings, voicemail and chat logs fall under it depends on your activity and your counsel's reading, so confirm the retention scope before you design storage. Ask the implementation partner how recordings are tagged, how legal holds are applied, and how deletion is blocked during the retention period. In a pilot, apply a hold to a test recording and confirm that automatic deletion skips it.

Why 911 requirements come before platform selection

Direct 911 dialing, central notification and dispatchable location are design inputs, not features you add later. They change the dial plan (which prefixes reach emergency services without a trunk prefix or access code), the trunk design (which carriers and numbers carry emergency calls and how their location data is passed), and the site layout (where phones sit and how each phone is mapped to a physical address). If you pick a platform first and then discover these needs, you may find that the dial plan or trunk model has to be rebuilt. Settle them first, then choose the platform that can meet them. The two US rules buyers should review with counsel are Kari's Law and RAY BAUM's Act. In plain terms, Kari's Law requires that multi-line systems let users dial 911 directly without a prefix or access code, and that a notification be sent to a designated central location when 911 is dialed. RAY BAUM's Act extends location requirements so that the dispatchable location of the caller, meaning the street address plus floor, suite or room where needed, accompanies the call.

Remote and non-fixed phones add a second decision. A softphone on a laptop or a desk phone at a home office does not sit at a fixed address, so the system needs a location method that can deliver a dispatchable location for those endpoints. Confirm with your 911 service provider which method they support, how the user updates location, and what happens when a registration moves across networks. You also need to decide how that method is tested and documented. Plan test calls from each site and from representative remote endpoints, record the dispatchable location each one delivers, and keep the results with the dial plan and change records. Ask your 911 provider and counsel to confirm the current rule text, the Federal Communications Commission (FCC) requirements that apply to your organization, and any state or local obligations, because those obligations determine the evidence you need to keep.

Once these answers are written down, they become requirements that any implementation partner can be held to. Ask the partner how they will map each endpoint to a location record, how they will verify emergency dialing before cutover, and who signs off on the test evidence. Confirm that the platform's trunk and dial plan design can carry the location data your provider needs, and budget for the recurring costs of 911 service and location maintenance alongside the platform itself. Treat the outcome of this step as a gate: no platform decision is final until the 911 design has been reviewed by counsel and the people who own your emergency response.

Which integrations to define before choosing a PBX

Phone systems rarely stand alone. Identity, CRM, ticketing, site systems, reporting and messaging each receive or send data that shapes the PBX design. Settle these integrations before choosing a platform, because each one determines the API surface, the connector work and who maintains it after go-live.

Identity and directory sync

Users, extensions and softphone logins usually come from a directory such as LDAP or Active Directory, or from an identity provider. Decide whether provisioning is manual, scheduled or event-driven, which attributes map to extensions, caller ID and voicemail, and how a leaver's extension is disabled. Ask the vendor or partner whether directory sync is native, how it is tested, and who updates the connector when the directory schema changes. Confirm the sync method against your own directory before you shortlist platforms.

CRM screen pops and call logging

Agents need the caller's record on screen, and every call should be logged against the right account. Define which CRM objects are matched (phone number, account, case), what call fields are written back (duration, disposition, recording link) and whether matching happens at ring time or after answer. Ask the partner which CRM connector is supported, whether it uses the CRM's documented API, and how field changes in the CRM are handled without breaking the telephony side.

Helpdesk or ITSM ticket creation

Support and facilities teams often need a ticket opened from a call, with the caller, time, queue and any recording reference attached. Decide which system owns the ticket, which fields are required and whether tickets are created automatically or by the agent. Ask whether the integration uses the helpdesk's supported API or webhooks, how duplicate tickets are prevented when a call is transferred, and who fixes the mapping after the helpdesk is upgraded.

Paging and site systems

Hospitals, schools and campuses may need paging, nurse call, door or bell systems to receive call-triggered announcements or to trigger calls. List each site system, its signaling method (SIP, analog, relay or vendor API) and the failure behavior if the PBX or the link is down. Ask the partner which interfaces have been deployed before, whether a hardware gateway is required, and which party tests the integration during cutover. Do not assume any site system integrates until your vendor confirms the interface.

Reporting and call data export

Management, compliance and workforce teams need call detail records, queue statistics and recording metadata in a predictable format. Define the reports, the retention period for each data type, the destination (data warehouse, BI tool or archive) and who may query it. Ask whether call detail records are exported in a documented schema, whether the export runs on a schedule or on demand, and how access to call data is logged for audit.

Email and chat notifications for voicemail

Voicemail and missed-call alerts sent to email or chat can expose caller information outside the telephony system. Decide which recipients receive notifications, whether audio is attached or only a link is sent, and which messaging platform carries the alert. Ask the partner how the mail or chat connector authenticates, where it stores credentials, and whether voicemail content can be excluded from notifications when the call may contain sensitive information.

How requirements change for a single site, multiple sites and a remote workforce

A single main office keeps the design simple, but it does not remove the hard requirements. Everyone sits behind one internet connection and one set of local network switches, so the main risks are local power, the single internet link and the number of simultaneous calls the trunks can carry. The first questions to settle are how many users and phones you have today and in three years, how many concurrent calls you need at peak, and whether you have one or more SIP trunk providers.

Users and devices: Count named users, desk phones, conference phones, paging devices and analog lines such as fax or elevator phones, since each needs a different provisioning path.
Trunk capacity: Confirm the number of concurrent call paths your SIP trunk provides and whether it is sized for peak business hours, not average use.
Local power and network: Decide whether the PBX server, switches and phones sit on uninterruptible power and whether the office has a backup internet path.
Emergency calling location: Even one building needs a documented dispatchable location for every phone, including phones moved between desks.
Backup and restore: Choose where configuration, call detail records and voicemail are backed up, and test a restore onto spare hardware.

Verify by placing a test call from every trunk and a 911 test call from a non-listed desk, then confirm that the trunk fails over or that the call path is documented if the internet link drops.

How to verify operational requirements: availability, monitoring, lifecycle and support

This table lists the operational requirements to settle before choosing an open-source PBX, with the concrete test that proves each one works. Read it as a sign-off list: every row should end with a written target and a dated test result, not a vendor assurance. The main takeaway is that availability, recovery and support promises mean little until someone has failed a trunk, restored a configuration and rehearsed an upgrade.

Requirement	What to set and confirm	How to verify it
High availability and failover	Define which functions must survive a server, trunk or WAN failure, and who decides when failover is declared. Get the recovery targets in writing.	Run a failover drill with live test calls: power off the primary, confirm inbound and outbound calls, and time the switchover against the written target.
Monitoring and alerting for trunks and registrations	Name the signals to watch: trunk status, SIP registration counts, channel usage, call failures and certificate expiry. Set who receives each alert and at what severity.	Disconnect a test trunk and a test softphone on purpose. Confirm the alert fires, reaches the named on-call person and appears in the ticket queue.
Backup and restore of configuration and recordings	Specify what is backed up (dial plans, extensions, queues, IVR, certificates, database and call recordings), how often, where copies live and how long recordings are kept.	Restore the configuration and a sample set of recordings to an isolated host. Confirm dial plans load, extensions register and recordings play back, then record the elapsed time.
Upgrade and lifecycle policy	Confirm the Asterisk and FreePBX versions in use, their published support status at the time of purchase, and the upgrade path to the next supported release.	Rehearse the upgrade on a cloned system. Compare dial plans, 911 routing and call flows before and after, and keep the rehearsal log with the change record.
Change control for dial plans	Decide who may edit routes, inbound numbers, emergency routing and time conditions, and what approval and rollback steps apply.	Make a test change in a staging system, approve it through the agreed workflow, then roll it back. Check the audit log shows who changed what and when.
Documentation	List the artifacts you expect: network diagram, dial plan map, 911 location records, runbooks, backup schedule and contact tree. Agree who keeps them current.	Hand the documents to a staff member who did not build the system and ask them to place a test call and restore one setting using only the runbook.
After-hours support with defined response expectations	Write the severity levels, contact channels, escalation path and response expectations into the support agreement. Confirm who answers outside business hours.	Review the support contract against the written severities. Open a test ticket after hours and confirm it reaches the named engineer through the agreed channel.

How to run the requirements workshop in sequence

The sequence moves from who and where the phones must work, to the legal and operational obligations, then to the technical design, so each later decision rests on written answers from the earlier ones. The final output is the signed requirements register that a partner can price as a fixed-scope quote.

Confirm users, sites and regulatory scope
Start by listing every user group, every physical site and every remote or home location that will place or receive calls, with headcount and the sector rules that apply to each. Compliance and the business owner sign off on the scope, because later steps depend on which sites and user types exist. Close the step with a site and user register that names each location, its address for emergency purposes, and the regulations that govern it. The step is done when compliance confirms that no site or user group is missing.
Define 911 and call recording obligations
Next, document what emergency calling and call retention must do at each site and for each device type, including fixed desk phones, softphones and remote staff. Compliance and legal review the obligations, and the network lead confirms how location data will be maintained for each endpoint. Ask the partner and your counsel to confirm the current requirements for your jurisdiction, since the rules and their test expectations are specific and should not be assumed. Close the step with a signed emergency calling and recording statement that lists retention periods, access roles and the test evidence you expect to keep.
Settle trunks, porting and dial plan
Document the carriers and SIP trunks you will use, the number blocks to keep, the porting order and the dial plan for internal extensions, outbound routes and emergency routes. The network lead signs off on capacity, failover paths and carrier contracts, while the telecom or service owner signs off on porting dates and numbers in use. Record the number inventory, the trunk capacity per site and the dial plan map. The step closes when the network lead confirms that every number has an owner and a route, and that porting risks are listed.
Specify queues, IVR, integrations and softphones
Describe how inbound calls are answered, queued, routed and reported, including IVR menus, after-hours handling, voicemail and any CRM or directory integrations. The contact center lead or operations owner signs off on call flows, and the application owner signs off on each integration's data fields. Include the softphone and desk phone models, the operating systems in use and how home workers connect. Close the step with a call flow document, an integration list with data direction, and a device inventory that the partner can estimate against.
Set availability, security and monitoring targets
Define the availability goals for each site and service, the survivability expected when a WAN link fails, and the controls for SIP exposure, administrator access and encryption. The security lead signs off on the access model, logging and vulnerability handling, and the infrastructure lead signs off on hosting, backup and failover. Record the expected behavior during outages in writing, along with the monitoring and alerting you will require. The step closes when the security lead accepts the control list and the infrastructure lead confirms where the platform will run.
Agree support model and approve the register
Finally, define who responds to incidents and changes, the hours that must be covered, and how Asterisk and FreePBX upgrades will be planned and tested. The IT service owner and procurement sign off on the support model, and the executive sponsor approves the full requirements register. The output is one signed document that combines all prior step outputs, lists open questions and states the acceptance tests. This register becomes the basis for a fixed-scope quote, so any change after sign-off should go through a written change request.

What buyers ask before hiring help with phone system requirements

How much effort does it take to settle phone system requirements in-house?

Settling requirements in-house usually takes sustained time from people who know the sites, the carrier contracts, the existing phones and the applications the phones must reach. Most of the work is collecting facts: a list of users and locations, current trunk and number inventories, call volumes by queue, the recording and retention rules that apply, and every system that needs a call event or a screen pop. Your staff must be able to answer these questions accurately, because a missing site or an unlisted integration tends to surface later as a change request. Plan for the people who own telecom, network, security and the business owners of contact center or clinical lines to be available for review sessions.

What drives the cost of phone system requirements work?

The main cost drivers are the number of sites, the regulatory scope and the number of integrations. Each additional site adds location data, trunk and emergency routing questions, and survivability decisions. Regulatory scope, such as 911 obligations, call recording retention or health information in voicemail, adds design and evidence work. Each integration with a CRM, paging system or directory adds discovery and interface definition. Requirements work is typically a one-time cost, though changes discovered during build can add to it. Ask any quote to itemize discovery, design documents, test plans and workshops separately, and to state what is excluded.

How long does the requirements stage take for a phone system?

The duration depends on how many sites, users and integrations are in scope, how complete your existing documentation is, and how quickly your stakeholders can decide. Organizations with clear carrier contracts and an up-to-date inventory move faster than those that must rediscover their own telephony. Decision cycles on recording policy, 911 location and queue design often take longer than the technical discovery itself. Ask any partner to show the phases, the stakeholder sessions they expect, and which decisions must be made before the design can be frozen.

Can we define phone system requirements without an implementation partner?

Yes, many teams document their own requirements, particularly for a single site with simple trunking and no contact center. Outside review is most useful for areas where mistakes are costly or hard to see from inside the organization: 911 and dispatchable location design, SIP exposure to the internet, call recording and retention obligations, number porting order, and high availability for critical lines. Independent review also helps when the requirements will be used to compare bids, because a neutral reader can spot gaps that the people who wrote them tend to miss. DeployOpen can plan, document and review these requirements as part of a fixed-scope engagement, but the regulatory interpretation and carrier obligations remain your responsibility to confirm with counsel and providers.

What does a partner need from us to produce a written scope?

A partner needs enough factual input to write a scope that both sides can hold to. Typically that means a site list with addresses and user counts, current trunk and number inventories with carrier names, a description of call flows including queues and IVR menus, the recording and retention rules that apply, and a list of systems to integrate with their owners and access methods. It also helps to know which sites must survive a WAN outage, what your support hours are, and who signs off decisions. Missing or inconsistent inputs are normally resolved during discovery, but they should be listed as open items in the written scope so that the quote reflects them.

Can 911 requirements be signed off without legal and carrier input?

No. A 911 requirement cannot be signed off by the technical team alone, because it depends on legal obligations and on what your carrier and emergency service providers can deliver. Your counsel should confirm the applicable rules for direct dialing, central notification and dispatchable location for each site and for remote staff. Your carrier must confirm which numbers, trunks and location methods they support and how they test them. Engineering can document the design, the test plan and the evidence, but the sign-off belongs to the people accountable for the obligation. The companion topic on 911 compliance for open source PBX covers the rules in more detail.

Which phone system requirements need security review before we choose a platform?

Any requirement that exposes SIP signaling or media to the internet, stores call recordings, or carries health or financial data in voicemail needs security review before platform selection. Typical items include remote registration and softphone access, encryption of signaling and media, admin access for the PBX and its management interface, log retention, and who can listen to recordings. Where call data falls under a regulation, such as the broker-dealer record retention rule or the HIPAA technical safeguard requirements for transmission security and audit controls, have compliance staff map each requirement to a control and an owner. Those mappings become the evidence an auditor will ask for later.

How DeployOpen scopes, delivers and supports phone system selection and implementation

DeployOpen plans, implements, integrates, hardens, documents and supports self-hosted open-source platforms inside your own infrastructure, including cloud accounts, data centers or air-gapped networks. For a phone system requirements checklist, we turn your sites, users, trunks and compliance obligations into a written scope before any build work starts.

How we scope

We map users, sites, call volumes and existing trunks into one written requirements document agreed before work starts.
We record which 911 obligations apply to each fixed, non-fixed and remote phone group, and who owns each location update.
Engagements are fixed-scope, so deliverables, timelines and exclusions for queues, IVR, recording and integrations are stated in writing.

How we build

We deploy the PBX platform in your environment, configuring trunks, dial plans, queues and IVR to match the agreed requirements.
We set up SIP security, registration controls and recording storage according to the retention rules you confirm with counsel.
We test emergency calling paths, failover behavior and integrations, and record each result as evidence for your review.

How we hand over

We deliver architecture, configuration, dial plan and runbook documentation so your team can operate the system without us.
We walk administrators through provisioning, number porting steps, change control and the 911 test procedure you will repeat.
We provide compliance evidence packs that support your assessors, while noting that independent auditors issue any formal attestation.

How we support

Ongoing support, upgrades and continuous testing are available as retainers after handover, with scope set in writing.
Retainers can cover upgrade planning, dial plan changes for new sites, and periodic re-testing of emergency calling paths.
Quotes follow from the written scope, so ask each partner to itemize build, testing, documentation and recurring support separately.