I read an article this week that PTT over a cellular network is completely different than for Nextel's network. The biggest drawback (aside from people having the equipment to actually carry on the conversation) is that it will take almost as long to use the PTT as for the cell call to go through. Nextel, OTOH, has instant communication via the walkie-talkie.
This article also stated that at most, Nextel has about 18 months before SPCS, T-Mo & Verizon catch-up completely.
Anyone else heard this stuff?