Marc - When I was researching cell phones before our recent trip on the PG, I found this web-site with a very informative series of articles on international cell phones:
http://www.thetravelinsider.info/2002/0308.htm

We ended up buying a quad band GSM phone (Motorola V600) and buying a SIM card for French Polynesia. We can buy SIM cards for other parts of the world when we need them. It is certainly worth checking out the alternatives to Cingular, since the rates can vary enormously (we paid about 40 cents per minute for outgoing calls and nothing for incoming calls while Kathy & Frank paid nearly three dollars per minute on T-Mobile for all calls!!).

There are a number of good sources for buying or renting international cell phones, including:

http://www.telestial.com
http://www.planetomni.com

Another thing to investigate is the call-back service offered by a number of companies. If your plan allows free incoming calls, then the call-back service can be a great deal. We used this one when we called home to our housesitter every day:

https://www.gphone.com (The name of the company is GlobalPhone.)

Finally, there are services providing service for calls from the U.S. to international phones for rates which are far better than any of the big carriers offer. That works very well if you have free incoming calls on your cell phone (very common when you buy a regional SIM card). We liked GorillaMobile:

http://www.gorillamobile.com Their rates for calls to French Polynesia from our home phone (and the neighbors' home phones in case of emergency) were about a third of the best "special international rate" offered by our AT&T long distance carrier. Definitely worth a look.

Have fun.

Cheers, Fred