Okay, so using an American mobile phone in London is tougher than putting NAT sound that Parkhurst likes into your TV packages.
It looks like AT&T/Cingular and T-Mobile have the best phones for overseas. First thing you'd need to do is figure out if they are quad band though. After figuring that out, you need to decide if you want to pay $2.99 a minute to call back to the US or receive incoming calls. If you don't, you need to get a SIM card that can go into your phone. In order to do that you need to get it unlocked by a few different services.
So as I said, that's the easiest option for using cell phones in England. Other cell phone carriers are much more difficult. So instead of killing myself doing this I decided to ask some students of mine who spent a semester abroad in London what they did. Below is an e-mail exchange I had with Mike Lurie on cell phones in London. For our purposes I think what he suggests will probably work best.
We went through a company called Piccell for our cell phones. BasicallySo there you have it -- I think pay as you go phones are probably the best option for cell use. It's basically a phone and a calling card and that's it. I used one when I lived in London and it worked very well.
you order them online and they get sent to you before you leave and you
send them back when you get home. It was fairly priced, and Piccell to
Piccell calls are free, except I don't know if it would work out for such
a short term trip. I would suggest buying a "pay as you go" phone when you
get to London. There are tons of stores around that sell phones for 10-20
pounds. You can top up in many stores as well, and just pay for minutes as
you use them. That is probably your best route.