Locks- don't bother. If any of the luggage handlers wanted into your suitcase they could use the universal suitcase key. So you are not going to prevent much that way. As Annies pointed out DO NOT put any valuables into your checked luggage. We take one or two carry ons for any camera's, jewlery and travel docs (passports etc) so that we don't have to worry about the checked luggage. They are not going to steal your clothes. In those same carry on's pack a swimsuit and a change of clothes for the first dinner since your luggage may not get to your room until late AND you may want to change for dinner or hit the pool if it doesn't come early.
Cell phones- No, you can not use them on the Ecstasy yet. not sure why you would want to. You can use them while in port in Galveston and for a little ways out into the gulf. But that's it. You can use them again in port in Cozumel and Progresso, but beware the international roaming costs (you may want to call your cell service provider and see what the charges would be.)
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013