Bought an O2 PAYG sim on ebay for coppers. Works fine (O2 no longer officially selling Classic PAYG).
Anyway, all set up, no bother, but one question: how often do I have to use the (spare) phone with that number to keep it valid? Is it 3 months, 6 months, or what? I ask as in the past I had such a spare phone, and when I went to use it it'd been cut off!
I'm sorry but I have re-read the terms and conditions and have given you the wrong information.
I cannot see any details about how often you need to use the phone to keep the SIM active but you do need to top up at least £10 every 6 months. You lose any credit that you have not used, it is not carried over.
To my mind, you may as well use the £10 credit, that way you will be sure to keep the SIM active and you won't be paying 02 for nothing.
As I understand it you only lose the credit if the phone is disconnected. This is rather worrying as I have £72 credit on mine and no way will I use that much within 6 months. I don't mind sticking a tenner on every now and then but I would hate to lose my credit. I have never lost anything before.
At that rate you're better off buying a different SIM where you don't need to top up to keep it live. I've been with Tesco for years and haven't paid any money in for at least 5 years and only ever use it for receiving calls and texts.