Cellphone only work were there can be cell towers (I know, I design the cell towers for a living). SO, out in the ocean, no, the blackberry won't work. UNLESS, Carnival has installed cell phone repeaters on their ships (I tought someone in this forum had mentioned they were planning it). If they did, then the phone would work as it does on land. You would have to call Carnival and ask. But be aware that even if they did install them, the charges could be high. Can she keep in touch via email? Or instant messaging? If so, she could go to the internet cafe, pay for a block of minutes and use their computers.
The other option is to wait unitl to get to your ports, but Nextel may not have service in your ports. (Grand Caymen may have service.)
Then, the most expensive way is to use your cabin phone for ship to shore call. Very expensive, but if she HAS to call in, that would be an option.
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