[RTuesday]

There isn't really any need for dual-sim phones within the US, because the number of people who need access to two US GSM networks for any reason is tiny.

There might however be a niche market in the border areas. On the southern border, combining AT&T (or an MVNO) with Mexico's Telcel (has UMTS 850) or Movistar would appeal to some cross-border commuters, although to be honest the market isn't really that sophisticated, most of them just know their minutes go faster when roaming over the border without really having any idea of the true cost. It would need a lot of educating to develop a market, and mostly in Spanish.

On the northern border, again commuters would be a small market but having a number from the "wrong" country while roaming is less of an issue there (because they're both in country code 1).

Even now the US (mass market) still hasn't really grasped that you can get a phone from anybody other than a carrier (contract or prepaid). Unlocked phones are a geek thing, not mainstream.

Rob