After confusing myself on the Internet for a few hours, I'm turning to the collective wisdom of NSC for help.

I lost my phone (iphone 5) on my stag do over the weekend. I've blocked it ok, but as I've still nearly a year left on my contract and no insurance, Orange/EE want over £300 to give me a new handset. They've agreed to send me out a new SIM for free (I've persuaded them to send me out a microsim and a normal one) which I should get tomorrow and then need to activate once I have it in a phone.

I thought I had an old iPhone 4 I could use for the next 10 months till my contract is up but I can't find that for the life of me. So the question is - if I can find someone else with an old iPhone 4 or 3 can I just use that? Would I need to get it unlocked and if so, how? Are there any other easy (and cheap) options I'm missing?!