How do I keep my number when switching to SIM only?

Keeping your existing mobile number when you move to a new SIM-only deal is free and takes one to two working days. This guide covers the whole process: how to get your PAC code, how to hand it to your new network, and what to expect on the day your number transfers. It was last reviewed in July 2026 against Ofcom's current switching rules.

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Reviewed by: Phil Brown, founder of SIM Only Finder. Phil previously worked in UK mobile retail at Three UK, advising customers on SIM plans, contracts, and network choices. He has spent over a decade running consumer comparison platforms and reviews networks and SIM-only deals based on that hands-on industry background. About the author

Last reviewed: July 2026. Updated regularly to reflect current switching rules, network processes, and transfer timeframes.

How we put this guide together

To put this guide together, we reviewed Ofcom's Text-to-Switch rules in July 2026 and checked the PAC, STAC, and INFO shortcodes, the code validity period, and the number transfer timeframe directly against Ofcom's published guidance and each major UK network's own switching pages. Where relevant, we have drawn on our own experience of porting numbers between UK networks.

Quick Network Switching Tool

Select the network you are switching from and the one you are switching to, and we will give you step-by-step instructions for that exact switch.

Before you switch

Two quick checks save time later. Make sure your phone is unlocked so it will work on the new network, and confirm which SIM format your handset needs before you order. Our guides on how to check if your phone is unlocked and what SIM card you need cover both in a couple of minutes.

You do not need to cancel your old plan yourself. When your number transfers, your old contract closes automatically.

Request a PAC from your current network

A PAC is a Porting Authorisation Code. It is the code that lets you carry your existing number to a new network. It is a nine-character code, three letters followed by six numbers, and looks something like ABC123456.

The quickest way to get one is to text PAC to 65075 from the phone with the number you want to keep. This is a free Ofcom service and your network usually replies within a minute. You can also request a PAC through your online account or by calling your current provider.

Your PAC is valid for 30 days. Requesting it does not start the switch and does not cut off your service, so you can get the code before you order your new SIM. Nothing happens to your number until you hand the code to your new network.

Check whether you are free to leave

If you are not sure whether you are still in your minimum term, text INFO to 85075. Your network will reply with your contract status and any charge for leaving early.

If you are still in contract, you can usually still switch, but you may have to pay an early exit fee. Your network confirms any charge when you request your PAC. Separately, most SIM-only plans raise prices during the contract, which is worth understanding before you commit to a new one: see our guide to mid-contract price rises. If flexibility matters most to you, a 30-day SIM-only deal avoids a lock-in altogether.

Give your PAC to your new network

Order and activate your new SIM first. It will arrive with a temporary number, which is replaced by your real number once the transfer completes.

Give your PAC, your temporary number, and the number you want to keep to your new network. You can do this online, by phone, or in store, and many networks let you enter your PAC during the order itself. From that point the switch is in progress.

Keep your old SIM in your phone until it stops working. Your number stays live on the old SIM right up to the moment the transfer completes, so leaving it in means you keep receiving calls and texts in the meantime. When the old SIM loses service, move over to the new one.

After the switch, check for a final pro-rata bill from your old network and cancel any related direct debit once that bill is settled.

How long does the transfer take?

The transfer takes one to two working days once your new network has your PAC. You will lose service only briefly on the switchover, usually a few minutes, while your number moves across.

You need to be in the UK on transfer day for the switch to complete correctly. Weekend and bank holiday requests are handled on the next working day.

What if I want a new number instead? (STAC)

If you would rather take a fresh number and not keep your current one, request a STAC instead of a PAC. Text STAC to 75075 from your current phone. Your provider replies with your Service Termination Authorisation Code, along with any charges left on your contract.

Give the STAC to your new network in the same way you would a PAC, and they handle the rest. A STAC also closes your old contract automatically.

What happens if I change my mind?

If you never use your PAC or STAC, it simply expires after 30 days and nothing changes. Your existing service carries on as normal. If you still want to switch later, request a fresh code the same way and use it within its 30 days.

If you have already handed over your code but change your mind before the transfer completes, contact your new network as soon as possible, as it may be able to stop the switch.

PAC vs STAC: what is the difference?

Use a PAC when you want to change networks and keep your existing number. Use a STAC when you want to change networks and take a new number. Both codes signal to your current network that you are leaving, and both close your old contract once used. The only difference is whether your number comes with you.

Editorial policy

This guide is produced by the SIM Only Finder editorial team to help readers switch network and keep their number with confidence. Switching rules, network processes, and transfer timeframes are checked regularly and updated to reflect current guidance. Always confirm current terms directly with your network before switching.