This is correct but not for the reason the T-Mobile sales guy indicated. Its isn't a conflict with the devices so much as UMA or GAN relies upon a feature within the MSC or call server. It is more likely that the T-Mobile network topology is not configured in a way that allows a single MSC or call server to perform UMTS, 2G and UMA concurrently. The radio network be it UMTS,GSM or UMA/GAN is homed to a MSC call server that support your geographical area. UMA to GSM handovers are difficult. Put the soft handovers of UMTS on top of this and it becomes a nightmare to provide a level of service without tons of maintenance to prevent an obscene high number of call drops between radio technologies. Don't get me wrong, we still rock a UMA enabled BB Curve and for people without even 2G coverage at their homes (like my parents in Vermont) it serves them well. I just think everyone (users and operators) is better off using SIP, Skype, or Google Talk on UMTS.