Sorry my message wasn't quite clear. You will only be charged the ship's fees ($100 for unlimited use if that is what you choose) - there will be no additional charges through your home providers. The Mariner will have in-cabin access as well as wi-fi hot spots as Tom mentioned.
Just a tip regarding AOL - For some reason it is often difficult to connest directly to AOL on ship's (that is the service I have). So, pass on to your friend - if he is having difficulty connecting through AOL - just use Internet Explorer (or your msn connection) and then once online - go to http://www.aol.com
and sign on that way. Have no clue why this happens - but it can be annoying.