O2

Can't fault them. Friendly, Helpful, Easy to deal with, Speedy Action!

Basically we lost a phone somewhere, rang it a few times and had quite an annoying conversation with a youth offering to give me my phone back for £20. So immediately rang o2 where i was answered straight away by a friendly guy, took a few details, blocked the phone and sim from being used and even managed to make me laugh again in the process.
He told me a replacement sim would be with me in 10 days...less than 24 hours later here it is.
Been with o2 since i was twelve, have had some great offers and saved a lot of money with them, Don't intend to change provider anytime soon!