I've used my (2G) Motorola US-purchased AT&T (Cingular) phone in Singapore with no problem whatsoever. I would imagine that the added 3G frequencies will match as well.
Cheers.
Sorry brp, but GSM/2G and 3G are a totally different ballgame.
She basically needs to pick a 3G phone that supports 850/1900 if she wants 3G here.
Samsung's BlackJack II and the iPhone are two that are pretty much cover it all.
Sony's walkman 3G phones mostly speak 2100 which isn't going to help her here unless she's OK with Tmobile, and OK with waiting for a while (tmobile's 3g footprint is nowhere near as big as AT&T's, NYC and Vegas last time I checked).