Do not get the unlocked Z699 if you plan to use AT&T. It doesn't work on GSM 850 and AT&T is moving there now. In fact, they are sending to customers free phones to replace phones they sold such as the T68i with new phones that work on 850. GSM 850 is simply GSM technology operating in the Cellular (800 MHz / 850 MHz) frequency band. Both the technology and frequency band have been around for a long time, but only in 2002 were they combined.
In the U.S. prior to 2002, GSM technology only operated in the PCS (1900 MHz) frequency band. AT&T is making heavy use of 850 for GSM.
GSM 850 addresses the needs of carriers with Cellular licenses switching from other technologies to GSM.
Before the existence of GSM 850, the Cellular band was ... (continues)
ATT will not be discontinuing use of this band for one and a half to two years (we will ALL most likely have new and better phones by then). They would isolate almost 65% of the country if they shut this band down anytime soon.
The "alarmist" message is exciting, but the sky isn't falling (quite yet).