They work in some ports where there is a cell tower while your on the ship or on shore. To my knowledge they will not work at sea outside the range of a tower.
Cell means to work within a set area and when you leave the influence of that area your phone sarches for and trys to find the next cell (area) ergo the name cell.
Hope this helps. Phone calls using the ship long distance satalite comunication is about $9.50 a minute. E-mail parlor on some ships is about 75 cents a minute. Some ports have e-mail parlors at a cheaper rate near the port.
My cell worked in Puerto Rico ($.99/minute), but not in the Virgin Islands. Your best bet is a phone card. Try this - http://www.global-call.net/
There is usually something in your inflight magazine. Mel