Marc, I'm not sure how Cingular works, but while I was on the Navigator in Europe, my phone would always go to the local coverage while close to port or even close to shore. While it was getting the ships signal, the network would be something like CC 139 XX. Does your phone display what network you're on? If not, you may be able to program it to display the network.

Even while on the ship, my rate was $1.15 per minute outgoing. When picking up the local signal, my rate varied from $.35 in the U.K. $.60 in most other locations, to $.69 while picking up a Moracco signal while sailing through the straights of Gibralter.

I used the Telestial Passport SIM in my GSM phone.