You technically can text using the onboard communications system, but I wouldn't recommend it because your phone company will be charged astronomically high rates for each text or call you make, of which the charges will be forwarded onto your bill. Unless you have money to burn back at home or you must make the call immediately, wait until the ship reaches port, then get away from the ship (at least off the pier) and get a terrestrial signal and then text; the roaming charges will be far less at that point. As for calling cards; you will need to check with the country you are visiting and they're usually "pay as you go" in that the roaming charges are deducted from the card so as long as you remain in the country of issue.