I might be wrong about this but based on my research:
Any GSM Android phone would work worldwide (voice, EDGE) but no Android phone I know of would work with 3G throughout the world (only phones I know of that have pentaband 3G are iPhone4/Nokia N8).
HOWEVER, my Acer Liquid has 900/1900/2100 3G bands. The 1900MHz 3G band works with AT&T 3G here in the US and the 900MHz/2100MHz bands are very common throughout Europe/Asia.