Sony would love to be on Sprint and Verizon but those carriers have an ironclad control on the phones available for their networks. Sprint sold their soul to Apple for a chance to carry the iPhone and now have a lot of those devices they have sell, leaving little room in their portfolio for OEMs like Sony and Nokia that don't have a big brand in USA. Blame Sprint and complain to customer service if you care that much about a broad choice of phones (or consider switching to a GSM based carrier)
Ah, i did not know that. Thanks for clarifying. Although what you said does make it seem like there wont be a sony phone on sprint anytime soon. Ah well