Do not go with O2!!!!!! Avoid at all costs!!!! My mum took out a sim only contract with 02 to save money on her existing pay as you go..... Whilst using her existing credit on her old sim 02 took out over £200 in her account! !!! For a sim card that hasn't been used or registered! !!! Two weeks later she has had no response and the customer service has been ridiculous. ....