I have Cingular wireless as my provider. I was on a Princess cruise in May and used my cell quite a bit on or very near the boat. Unfortunately it did not often work at sea or on certain islands. The islands I did get service from (even if I was on the boat) were Puerto Rico, St. Thomas and St. John. I was NOT charged any additional roaming, extended use fees etc. I was billed directly to my free weekend minutes. I was NOT able to use the phone however on St. Maarten or Antigua. The cruise returned to NY and I also got no service up the entire Atlantic coasrline.

Possibly I wasn't charged anything on the islands that the phone worked since they US territories.

Another idea is using the computer to place phone calls. I saw a gentleman in the atrium of the ship - area where there was free wireless internet access. He was talking on a call using a bluetooth headset possibly Skype or something similiar. This was during a time when I had absolutely no service myself.