T-Mobile USA now allows roaming in Europe!
http://prepaid-phones.t-mobile.com/c...llingRates.pdf
Not the greatest prices, and a very slipshod list (outdated network names, spelling mistakes, etc.) but I just tested it in Germany and it does indeed work. I wonder if the omission of the UK from the list is an oversight (Britain is also a T-Mobile country) or something that will be added later.