T-mobile sounds like a much better option, the i2000 is OLD (like August 2000 old) and doesn't do tri-band (or even dual band GSM) networks. It won't work in Japan but then again neither will any GSM phone. Pick something with today's technology.

On T-mobile most countries are $0.99, others are between $1.49 and $2.99 except for some places you don't want to be anyway...