3 offers a variety of sim only contracts from 30 day rolling contracts all the way through to 12 month contracts. Please note that 3 sim only sim cards will only work in 3g mobile phones. 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.