Keeping your numbers is usually the part of a phone system change that takes longest. To port phone number ranges to a VoIP provider you ask the new (gaining) provider to request them from the current (losing) carrier, and the losing carrier checks every detail against its records. Most delays come from a mismatch in those details. This guide covers the process, the paperwork and the common rejections, with notes for the US and UK.
Short answer: Confirm the new provider can serve the numbers’ area, get a copy of the Customer Service Record (CSR) or latest bill from the current carrier, fill in the Letter of Authorization (LOA) with the account holder name, service address, account number and PIN exactly as the carrier has them, list every number (including the main billing number if it is moving), and do not cancel the old service until the port completes. Test each number as it goes live.
Table of Contents
1. Check portability
Ask the gaining provider to run a portability check on every number before you sign up. Geographic numbers can usually only move to a provider that has coverage in that rate centre or area code, and some countries restrict moving numbers between areas or between fixed and mobile. Toll-free numbers follow a separate process; in the US that is a change of RespOrg.
2. Get the customer service record
The CSR is the losing carrier’s record of your account: authorised name, service address, billing telephone number (BTN) and every number on the account. Ask the carrier for it, or at least use the most recent bill. Most rejections are caused by filling in the port request from memory instead of from this record.
3. Complete the letter of authorization
The LOA gives the new provider permission to act for you. Copy these fields exactly as they appear on the CSR, including abbreviations and suite numbers:
- Account holder or business name
- Service address (not the billing address, if different)
- Account number, and PIN or passcode for mobile numbers
- Every number to port, and whether this is a full or partial port
- Name and signature of an authorised person on the account
4. Avoid the common rejections
| Rejection | Cause | Fix |
|---|---|---|
| Name or address mismatch | LOA differs from the CSR | Copy details from the CSR character by character |
| Wrong account number or PIN | Old bill or missing mobile PIN | Request current values from the carrier |
| Partial port of the main number | Moving the BTN but leaving other numbers | Port all numbers, or nominate a new BTN with the carrier first |
| Pending order on the account | Open changes or a disconnect request | Clear or cancel the order, then resubmit |
| Services on the line | DSL or alarm service tied to the number | Move or cancel those services first |
5. Plan the port date
In the US, the FCC requires simple ports to complete within one business day, but business accounts with several numbers are often not “simple” and can take one to three weeks. In the UK the gaining provider manages the request and timescales depend on the number type. Book the cutover for a quiet day, avoid Fridays, and keep the old phone system running until the port is confirmed.
6. Test on port day
As each number activates, call it from an outside mobile, check it reaches the right queue or IVR, send an outbound call to confirm caller ID, and test SMS if the provider supports it on that number. Only then cancel any remaining services with the old carrier, and ask for written confirmation that the account is closed.
If you are still choosing where the numbers will live, JustCall and CloudTalk both handle porting for business numbers; our reviews compare their plans and number coverage.
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Port phone number at a glance
Official documentation: FCC: keeping your number, Ofcom: switching and keeping your number, RFC 3261: SIP.
Related guides: Migrate PBX to cloud · SIP SRV records · VoIP codec bandwidth.
Frequently asked questions
How long does it take to port a business phone number?
A single number can move in one to a few business days. Business accounts with many numbers typically take one to three weeks, and longer if the first request is rejected.
Will I lose calls while the number is porting?
Not if you keep the old service active. The number keeps working with the old carrier until the switch, which usually happens within minutes to hours on the port date.
Can every phone number be ported to VoIP?
Most can, but the new provider must cover the number’s area, and some special or premium numbers and certain countries have restrictions. Always run a portability check before committing.
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