UMTS 850 in USA

[inquisitor]

It seems like my assumptions above are wrong. Wikipedia says:

AT&T Wireless launched UMTS services in the United States by the end of 2004 strictly using the existing 1900 MHz spectrum allocated for 2G PCS services. Cingular acquired AT&T Wireless in 2004 and has since then launched UMTS in select US cities. Cingular renamed itself AT&T and is rolling out some cities with a UMTS network at 850 MHz to enhance its existing UMTS network at 1900 MHz and now offers subscribers a number of UMTS 850/1900 phones.

So you either need another phone or settle for 2G only.