Things to know about 3G:
Cingular uses 850/1900 UMTS/HSDPA
T-mobile (US) will eventually use 2100 (with 1700 upstream) UMTS/HSDPA
The rest of the world uses 2100 (with 2100 upstream, I believe) UMTS/HSDPA
Thus, no, the N73 will not work on any 3G in the US. The only 3G S60 device is the N75. There were a handful of prototype N80s that had it, but that's it.