Here is what we know. Back before the first iPhone launched, Apple signed an exclusivity deal with AT&T. That deal is due to expire at some point in the relatively near future. When that happens, the iPhone will come to multiple US carriers. The questions on everyone's mind are; which carrier will be first, and when will it happen?
All Things D reports that Kaufman Brothers analyst Shaw Wu believes that T-Mobile is the most likely candidate to be Apple's first new carrier. His reasoning is difficult to argue with; T-Mobile's network won't require Apple to build an entirely new iPhone.
Odds are, a CDMA iPhone (for VZW or Sprint) will take longer to launch than a T-Mo iPhone. Of course, VZW has nearly three times as many users as T-Mobile, so Apple may eat the cost and difficulty of making a new sort of iPhone for the huge user payoff.