[rrvo]

Using your US based phone overseas is normally going to run $2-2.50 per minute and your data charges are likely to be horrendous--call your provider and ask what their coverage and charges are in the countries you'll be visiting.

I've had better luck using an unlocked sim-card-based gsm phone--usually cheaper if bought overseas, particularly if you're headed for the more developed parts of Asia. Your cheapest rates will be found by buying a local SIM card (many times you can also find a sim card that will provide data so you can also access your email and run Skype, Tango and other VOIP/video calling programs, which can also cut down on calling costs.

If you will move from country to country and need to be able to have associates reach you at the same number, you can use WorldSIM or something similar. (WorldSIM works well for voice but I haven't yet been able to use data with the service.)

I'll have the lowdown on Japan when I get back from there in May, 2012, but my understanding is that, while they are basically CDMA, Japanese CDMA services won't "shake hands" with US CDMA phones.

Good luck!