You'll find a lot of information in the Travel Technology forum.

Truphone is a possibility and their SIMs are sold on board BA flights. There have also been free Truphone SIM offers. However, IMO there are better value alternatives.

It depends how long you will stay and how you use your phone. It may be worth considering T-Mobile USA after all. Their SIM only deal would cost $100 for a year. You get a large number of minutes and your number doesn't expire. Top it up after a year - ISTR that $10 does the trick - and you keep your number.

For less busy use, you might think about SIMs from e-Kit. There are several variations. Generally, you don't get charged for non-use if you make at least one call or send one text every nine months. Best all round prices are at http://www.lonelyplanet.ekit.com/eki...ePurchase/Sims

E-Kit SIMs can also be bought at eBay 'buy now' at decent prices.

All of this presupposes you have an unlocked mobile.

Take an FT stroll through the Travel Technology forum for (a lot) more info.