Alaska is a mecca for cell phone service. Just about everyone carries one- or a blackberry or the like. You should be able to use your cell phone in all Alaska ports, except maybe Skagway - (there you can use celluar one towers but there is difficulty with others) The cell phone providers have been working on upgrading thier service, so both local users and visitors on the ships can use the service. Since you sail from port to port at night and visit ports during the day, you should not be without service for very long at a time.
Hope you have a wonderful trip.