O2 offers a variety of sim only contracts from 30 day rolling contracts all the way through to 12 month contracts. O2 sim only contracts deals are also avilable for Iphones, blackberrys and Smartphones. A sim only contract is whereby you decide that you dont need a new phone because your current phone does its job perfectly. With a sim only contract you dont get a mobile phone and instead you get just the sim card. With no 'free' expensive phone in the deal, these savings are then passed on to you - the customer - meaning you can lower your monthly phone bills as well as getting a more attractive deal.