Bringing this thread back to the top, I have actually the same question as the OP. I'm looking for a phone that can be used in Japan, Korea, EU. US usage not necessary as I have Sprint in the US with mainly voice use (no data services required really).

To summarize alanw:
UMTS2100: Japan, Korea
US: GSM 850/1900, UMTS850/1900
Europe: GSM900/1800, UMTS2100

I used the phone finder at GSM Arena to locate GSM + UMTS (3G) phones and came up with a rather huge list. Since they don't allow you to restrict by price I tried weight and came up with a list of about 55.

Before I go digging through the list does anyone know off-hand of any cheap ones? I believe someone mentioned the Samsung Z150. I'd like light-weight, flip-up for pocket carry (but completely optional) and I'd like to spend less than $200, ideally less than $150 even for it.

Sony Ericsson K610, K618, W660, W880, V630, T650
Samsung Z150, Z230, Z240, Z330, Z370, Z500, Z510, Z550, Z560, Z620, Z650i, Z720, ZV40, U700, F500, F510, F520, F700, i520
Nokia 6151, 6120 classic, 6500 classic
Motorola V1000
LG KU800, KU580, U300, U830, U880, U890, L600v, U310, KU250
i-mate Ultimate 8150, 9150
BenQ-Siemens S81, EF91, E81
O2 Ice
Sagem MY 800X
Sharp 550SH
NEC e373, e353
VK Mobile VK7000
Toshiba TS705
Pantech U-4000, PU-5000
Sagem my600X, my600v