Text PAC to 65075 for your Tesco Mobile PAC code. Then keep your Direct Debit until the final bill, cancel Tesco Mobile Protect separately, and reclaim PAYG credit.

To get a Three PAC code, text PAC plus your date of birth (DDMMYY) to 65075, e.g. PAC060385. Got several numbers? Use My3 or call 0333 338 1082.

Text PAC to 65075, call 43431 or request it online to leave giffgaff. Joining? Enter your PAC before 3pm, and be in the UK on transfer day.

Switching to Lebara? Get a PAC, activate the SIM and fill in the port-in form at lebara.co.uk/portin. Here is which number goes where, and how to leave Lebara.

Text PAC to 65075 from your Vodafone phone for a free code. Here is what changes if you are moving to VOXI or Three, and how to check leaving fees first.

Text PAC to 65075 from your EE phone and the code arrives in a minute – unless the account is in someone else’s name. Here is what to do then.

Text PAC to 65075 from your O2 phone and the code arrives in a minute. Here is what to do when it does not, and what to check before you switch.

No UK network lets you pick your own mobile number. Here is why, and the one route that actually lets you choose the digits.

Text PAC to 65075 and your network must send the nine-character code back within a minute. Here is how to use it, what happens on switch day, and what to do when it goes wrong.

Why eights and 786 command a premium on UK mobile numbers, why fours narrow the market, and what cultural demand really does to price.