In the "My Cruise Travel Kit" I received from
DCL prior to my sailing, on page 28, it states this:
SHIP PHONE NUMBER
While onboard the
Disney Magic, all guests can be contacted by calling 1-888-DC-AT-SEA (322-8732). Calls will be immediately transferred to your stateroom. Messages can be recorded via voice mail. Keep in mind that hefty ship-to-shore (satellite) telephone rates apply. Please check prices listed on your stateroom telephone for details. Toll-free (1-800, 1-888) calls cannot be placed from the ship. Satellite telephone rates can be
significantly higher than traditional long distance.
(italicized words were italicized by DCL themselves, not added by me)
So, one way or another, someone is paying if someone calls you on the ship. Either the caller or the callee.
HTH