Being in Real Estate.... The palm devices might be best due to the key boxes using the IR ports.
I heard some might go bluetooth, but until it is used more widely, the Palms seem to have the market cornered.
GSM only means something if you travel internationally. Otherwise, choose the best network for where you are. In fact, the national Verizon CDMA network and its high speed EVDO network are both bigger than the AT&T network and high speed data coverage areas.
AT&T is also about to lose the claim that they have the largest customer base in the US. Once the Alltel merger completes in December, Verizon will have more customers, a larger National Network, and a lager (and faster) high speed network.
Take into consideration Verizon's in-house technician's and warranty services and they usually always trump what AT&T offers. AT&T uses a mail-order warranty service, and does not offer any sort of New-Every-Two credit when it is renewal time either.
Well, that's my speil. Sorry. lol