GSM unlimited voice/msg/data is finally available in the US
 

Success with Simple Mobile!! - As long as you're in an area with native T-Mobile coverage, this might be something to consider. Unfortunately voice is required in order to get anything else, so it can be a bit expensive unless you plan to utilise everything. Only go for it if you are sure T-Mobile has good enough coverage for your needs as the SIM has no roaming.

As long as you're in urban areas T-Mobile will do pretty well. It does not do well in rural areas generally though they do have some limited roaming with AT&T.