Changing networks but keeping the same mobile phone number
If another service or network would suit you better, you can switch and keep your existing mobile number.

Number Portability or Migration?
Number portability is taking your number from one mobile phone network to another.

Number Migration is taking your number from one contract to another within the same network. Some Service Providers will make a charge for this service, or may not even allow it at all.

Orange is the only network that lets you migrate a number from PAYG to Contract.

You can only take a number to a PAYG connection if you are joining Orange or T-mobile.

Sim Cards
The SIM card is provided (and owned) by the network or service provider and contains your mobile phone number and all the details of your subscription. In effect it is the phone account's identity to the network. Remove the SIM card from one handset and insert it into another and you have moved your mobile number and bills to the new handset.

Or Can You?
One2one and Orange put software in all their phones to stop you using any other network's SIM in them. This can be removed (it is called the SIM lock or SP lock) and usually the network will make a £20 to £35 charge for issuing the release code. There are third-party companies that unlock handsets more cheaply, but you may have to send your handset to them. They can't always simply tell you the unlock code.

Vodafone PAYG phones may not only be locked to Vodafone, but may be locked so that they won't accept a sim card that isn't on the same tariff, or possibly not even any other sim card. Again, a third-party company may be able to resolve this problem.

Mostly, however, you will want a new account for an existing phone, or maybe a new phone too.

Get a new mobile, cheap or for free
When you change to another network, this counts as a new contract to them, and this means a subsidised handset. Even if you have a handset you could use, it is probably in your interests to get a new one, cheap or free (depending on the model you choose and the contract you join).

How To Move
You can find more information on each of the operator sites, simply purchase the mobile you want and follow the instructions where at part of the checkout process you will be given the option to keep an existing number.

The fine print
Don't cancel the old phone! You must have an active mobile phone number up and running - which has to be active during the week or two it takes to transfer your mobile number to the new account or network.

Suspended numbers have to be re-activated by your old service provider/network before any transfer can take place.

Don't forget about any fax and data numbers when requesting a number transfer.

To start the process, ask your current service provider for a nine-character Porting Authorising Code (PAC), which you take to your choice of dealer, and is the approval certification that makes it all happen.

What Happens Next?
After a credit check, providing there are no outstanding bills payable to your old account, the request is processed between your old and new networks, and you will be given a date of transfer of your number.

The single PAC covers activation of your new account and disconnection of your old and you will receive communications from both parties confirming your requests.

How Soon Can I Get On With It?
If you are within the intial contract period (normally 12 months) you will have to pay the rest of the period's line rental before your network will release you, and you must have no outstanding debts with them, but apart from that, it should be possible straight away.

Please make sure you check with your current Service Provider, as they may make a charge to release your number.

Customers migrating onto O2 or Vodafone will probably have to pay a fee to the dealer they are buying from for the transfer paperwork.

How long can I leave it?
A PAC is valid for 30 days from the date of issue, and after that, you'd have to ask for another one if you haven't used it. When moving to a new network, you have to tell them you are bringing a number with you right at the outset. Orange will allow you to bring a number later if you take out a contract (not PAYG). It's wise to warn them that you may be planning to do this, though.

Important
Transfers take from 3 to 10 working days to complete, during this time the account you are transferring your number from still has to be live. Don't cancel the old account before porting a number. In certain instances your present or new Service Provider can reject a number transfer.

Please make sure you check with your current Service Provider, as they may make a charge for you to take your mobile away to another Network/Service Provider, especially if you still have a contract term to expire, you will be liable for the cost of the duration left.