Verizon, Sprint, Alltel, US Cellular, etc... you can roam on all those networks.
Correct me if I'm wrong, but I think that only Verizon and Sprint have their own CDMA networks and Alltel and USC resell one of the above. -- Ask me no questions, and I'll tell you no lies... A MESSAGE to the RIAA and the MPAA: You shouldn't wound what you can't kill...