also, just to answer the original question, PTT support on the BlackBerry, thus far, is being provided by Kodiak Networks. for BlackBerry devices, they service Cingular, Alltel, Orange UK, and AirTel (per their website). i'm sure we'll see the PTT service available on all of these carriers. aside from them, probably not... but who knows.

what would be more interesting with Sprint is if they're going to phase out Nextel's DC service in favor of their Ready Link PTT service, or if they are simply going to push both as competing products.