If you're looking for a smart phone to use on PPC, see below for some information. Any phone must have a clean Vzw ESN to be used on PPC.
--Any Vzw 3G (no 4G) Android, WinPho, WebOS, or WinMo smart phone will work 100% on PPC with no modifications.
--iPhones (4 & 4S) are not "banned", but are not "supposed" to be used on PPC, although there are plenty of forum postings reporting that they work fine. There have been warnings stating that iPhones "could" be deactivated by PPC or Vzw, but so far, there have been no reports of that happening.
--Blackberries require loading of service books to get MMS and data to work properly on PPC, but lots of people are able to do it successfully, so that everything except BIS works.
--4G phones can be made to work, but it isn't easy, and even then only 1x or sometimes 3G data speeds can be achieved, but never 4G, since PPC doesn't currently support 4G. There are massive threads on various forums about trying to make modifications to get 4G phones to work fully on PPC. As an alternative, a flashing service might be able to get 4G phones to work on PPC.