::2100 Mhz is only the default operating frequency for UMTS in Europe; although I believe they have relaxed this so it can now be deployed on 900 and 1800 Mhz. networks as well. The larger issue is that UMTS requires one 10 mhz. contiguous chunk of spectrum for one channel, whereas Qualcomm CDMA requires 2.5 for a single channel; although this is not as wide as a UMTS channel, it allows operators more flexibility with limited spectrum... that said, everyone is moving towards LTE now, both on CDMA and UMTS sides, and that can be deployed with as small as 3 Mhz, although in practice 10 Mhz or larger channels are primarily used. Also IS-95 CDMA and GSM-based standards have completely wiped out TDMA (D AMPS) in the Americas  most (if not all) networks that were previously TDMA have now moved to CDMA or GSM-based systems since 2009. I am no longer aware of any TDMA-based (D AMPS) systems in existence  one of the last ones being on the north slope of Alaska (ASTAC) which converted to GSM/UMTS a few years back.