I currently have an AT&T iPhone 3G and will be moving to the UK in a few weeks. I'm attached to my phone and would like to continue using it while I'm there on a carrier in the UK. Do I need to unlock the phone in order to use it there? If so, what networks am I limited to? I suppose I will be doing a month-to-month plan. Frankly, I don't use a lot of minutes or texts so that may play a role in who has the least expensive plan with "unlimited" data and a small amount of minutes/texts. Thanks!