T-Mobile's UnCarrier Initiative - I have been impressed by T-Mobile because of the recent consumer friendly initiatives.
Got a chance to use their free International Roaming and Unlimited texts with their Simple plans. Worked like a charm and no surprise costs. Yes they cap high speed data after 10MB and you need to buy extra packs after that (so you need to decide if a local SIM is better) .
This is the first time I have had such a pleasant experience with International Roaming.
Now just improve the coverage area map in USA and you will be the best in USA.