Prepaid? Post-paid? For how long?

Do you know which 3G bands your model supports?

T-Mobile, AT&T, Straightalk and H2O Wireless are the pre-paid options which I am aware of.

A specific recommendation may follow once people understand your requirements.

I've been using T-Mo pre-paid for ~ 8 years for my frequent trips to the U.S.; I now use the $2/day option for unlimited calls, texts and 2G data.