Depends on what you mean by on
cruise. You can get 3G/4G pretty much up and down the whole
east coast and most of the
west coast, up to 4-6 miles
offshore with a standard
cell phone. Further out you need a booster.
At
anchor you can use a long range
wifi and pick up the local Starbucks with having to go in.
Further that this you have to use
satellite (very expensive) or shortwave
radio (very slow).
If you want to read more there are a dozen threads or so that have covered the subject in great detail.