In short: Number porting is the process of moving your existing phone numbers from one provider to another when you change phone system. Your new (gaining) provider requests the port from your current (losing) provider using your account details and a letter of authority. Most UK geographic, non-geographic and mobile numbers can be ported if the details match exactly.
How number porting works
When you change phone system you normally keep your numbers. UK regulation requires phone providers to let customers take their numbers with them, so in practice your numbers stay with your business rather than with any one supplier.
The process always runs the same way round. You sign up with the gaining provider (the new supplier), give them details of your account, and they raise a port request with the losing provider (your current supplier). The losing provider checks the details against its records and either accepts the request and agrees a port date, or rejects it with a reason. On the agreed date the numbers are switched across within a set window during the working day. For ports into Teams Calling Plans, for example, Microsoft's UK guidance says ports run Monday to Friday between 09:00 and 17:00, with a porting window of two to four hours.
You do not need to contact your old provider to start a port, and you should not cancel your old service first. As Microsoft's own porting guidance points out, inactive or disconnected numbers cannot be ported, so cancelling early can cost you the number entirely. Your gaining provider, or we, will tell you when it is safe to close the old account.
If you are changing more than numbers, our PSTN switch-off checklist covers the wider move, and ISDN replacement options compares what to move to.
Which numbers can you port?
Most business numbers can move between UK providers. The type of number affects what you need to provide and where it can go.
| Number type | Examples | What to know |
|---|---|---|
| Geographic | 01 and 02 numbers | The most common port. Single numbers and DDI ranges can both move, usually together with the main number on the account. |
| Non-geographic 03 | 0300, 0333, 0345 | Calls to 03 numbers are charged like calls to 01 and 02 numbers, so they suit a national main number. Have your current provider's account number ready: Microsoft, for example, makes it mandatory for non-geographic ports. |
| Freephone | 0800, 0808 | Often used on a menu or call queue rather than a single person's phone. |
| Service-charge numbers | 0843, 0844, 0845, 0870, 0871, 0872 | Can usually move between UK carriers, but not every platform accepts them. Check before you commit. |
| Mobile | 07 numbers | Ported between mobile networks using a PAC code. Moving a mobile number into a desk phone system is a separate question: Microsoft, for example, only accepts mobile numbers into Teams Calling Plans in the US, Puerto Rico and Canada. |
Some numbers cannot be used everywhere. Microsoft, for example, does not accept numbers used for data connections such as broadband, and accepts fax numbers into Teams Calling Plans but does not support faxing on them. If you still rely on fax, plan for that before the port.
The porting process, step by step
A smooth port is mostly preparation. These are the steps we follow for every customer.
- Collect a recent bill from your current provider. It shows the account number, the billing or main number, the registered business name and the installation address.
- List every number you want to keep, including DDI ranges, fax numbers, freephone numbers and any numbers that only divert somewhere else.
- Check the account is active and that there are no open orders, moves or cancellations in progress. A frozen or locked account must be unlocked first.
- Decide on a full or partial port. A full port moves every number on the account and usually closes it. A partial port leaves some numbers behind, and not every provider or platform accepts one.
- Sign the letter of authority (LOA). This gives the gaining provider permission to request the numbers on your behalf. The name and address must match the losing provider's records exactly.
- Agree a port date and a time of day that suits you, and set up the new system so it is ready to take calls before that date. Leave enough lead time for a rejection to be corrected: Microsoft, for instance, recommends a target date at least 15 business days after submission.
- Freeze changes. Avoid moves, additions or cancellations on the old account while the port is in progress, because an open order can cause a rejection.
- Test on the day. Ring each ported number from a mobile, check menus and groups answer as expected, and check outbound caller ID.
- Close the old service only after every number is working on the new system.
Why ports get rejected
Rejections are almost always caused by small mismatches. The losing provider only tells the gaining provider the category of the problem, so each correction and resubmission adds time. Common causes are:
- The business name, address or account number on the LOA does not match the losing provider's records
- The main billing number is missing from the request, or the request mixes numbers from different accounts
- An open order, house move or cancellation is already in progress on the account
- Advanced features such as hunt groups or special routing are still active on the old lines
- The account is frozen (a protection some providers offer against unauthorised ports) and the freeze has not been lifted
- Two port requests for the same account were sent at the same time; providers process requests for one account one at a time
- The numbers are on a reseller's account, so the request needs the reseller's details rather than the network operator's
Porting a number away can also end other services tied to it, such as broadband or an ISDN service on the same line. Microsoft's guidance says these are disconnected automatically once the port completes, unless they are first moved to a number you are keeping, and the same risk applies whichever platform you choose. We check what else depends on each number before the port is booked.
Porting into Teams, 3CX, Forever UC and SIP trunks
Where the numbers end up changes who runs the port.
| Destination | Who raises the port | Things to know |
|---|---|---|
| Teams Calling Plans | You or we, through the porting wizard in the Teams admin centre | Microsoft becomes the carrier. Microsoft's UK guidance says ports take roughly 12 to 30 business days, partial ports are not supported, and freephone numbers are for auto attendants, call queues and conferencing rather than users. Microsoft also says it does not currently accept UK numbers beginning 0843, 0844, 0845, 0870, 0871 or 0872, so check before ordering. |
| Operator Connect | The operator | The operator ports the numbers to its network and assigns them to your Teams tenant. |
| Teams Direct Routing and Forever Teams | The SIP or Direct Routing provider | Numbers port to the carrier behind the Session Border Controller and are then assigned to Teams users and resource accounts. |
| Hosted 3CX or your own PBX on SIP trunks | The SIP trunk provider | 3CX does not hold numbers itself, so they port to the SIP trunk provider you choose and are routed to 3CX. |
| Forever UC | Forever Group | We port the numbers onto the service and set up the menus, groups and users that answer them. |
For BT Cloud Voice, our sister company Forever Communications Limited explains the BT process on BT Cloud Voice numbers and porting.
Avoiding downtime and how we help
How long a port takes depends on the losing provider, the number type and how many numbers and accounts are involved, so we never promise a date before the losing provider has confirmed one. What we can do is make the wait painless:
- Temporary numbers on the new system from day one, so staff can make calls and you can test everything before the port
- Diverts from the old lines to the new system while you wait, where your current provider offers them
- A phased plan for organisations with several accounts or sites, so ports for the same account do not collide
- A port-day checklist covering every number, menu and group, with caller ID checked on outbound calls
Mobile numbers follow a different route. If you are moving business mobiles between EE Business, O2 Business or Vodafone Business, you request a PAC code and give it to the new network. Forever Group's business mobile team handles those moves.
Contact us with a recent bill and the list of numbers you want to keep, and we will check them before you commit to anything.
Why choose your cloud phone system with Forever Systems
We are vendor-neutral. Forever Group supplies and supports several cloud phone platforms, so we recommend the one that fits how your organisation works rather than the one we happen to sell.
- Side-by-side comparison of hosted 3CX, Microsoft Teams Phone, Forever UC, Forever Teams and Webex Calling for your users
- Contact centre and call recording options matched to your call volumes and CRM
- Number porting, handsets and set-up handled for you, including the move off analogue and ISDN lines
- Connectivity checked so call quality is right from day one
- UK support for moves, adds, changes and faults
- For BT Cloud Voice, see our BT Business Partner site cloudvoice.cloud
We work with businesses, schools, charities and public sector organisations. We do not sell consumer phone services.
Want a vendor-neutral cloud phone system comparison and quote?
Tell Forever Systems what you need and we will come back to you by email with options, not a hard sell.
Contact usFrequently asked questions
Can I keep my business phone number if I change provider?
Usually, yes. UK providers are required to support number porting, so geographic, 03, freephone and mobile numbers can normally move to a new provider. The new provider raises the request, and your current provider checks the account details against its records before agreeing a port date.
How long does number porting take in the UK?
It depends on the losing provider, the number type and how many numbers and accounts are involved. Microsoft, for example, says ports into Teams Calling Plans in the UK take roughly 12 to 30 business days. We confirm a date only once the losing provider has accepted the request.
Should I cancel my old phone line before porting?
No. Inactive or cancelled numbers cannot be ported, so keep the old service running until every number is working on the new system. Close the old account only after the port is complete and tested.
What is a letter of authority for number porting?
A letter of authority (LOA) is a signed form that lets your new provider request your numbers from your current provider on your behalf. The business name, address and account number on it must match your current provider's records exactly, or the port will be rejected.
Can I port only some of my numbers?
Many providers allow a partial port, where some numbers move and the rest stay on the old account. Not every platform accepts one: Microsoft's UK guidance says partial ports into Teams Calling Plans are not supported. We check this before you order.