Using your smartphone in the US on vacation (T-mobile rocks)
This is something that has been discussed on forums everywhere and there is no real answer.
Just arrived in San Francisco with my swedish iPhone 4, went into a T-mobile store and bought a Monthly4G package for 50$, this gives me unlimited data, talk and text for one month.
Added 10$ and I got free text and landline calls to Sweden.
The only bad thing is that T-mobile 3G network uses a frequency that the iPhone (and many smartphones) cannot use so I’m limited to Edge data transfer.