I also have Verizon Wireless, and called them about using my cell phone while cruising. It is do-able, but the per minute rate can be costly. Call them and tell them where you are going and what ship. They do something on their end, and then you are charged depending on where you are. If you just use your phone to call home to check on things, a minute or two, you will be fine.
As for reception, I had no problems, except when in the cabin. Go up on deck or wait until you are on shore to call.
Sitmar Fairwind - June 1985, Sept. 1985, June 1986
Sitmar Fairsky - June 1987
Carnival Fantasy, March 2002
Carnival Fascination - April 2004, October 2005, Dec 2006
Sovereign of the Seas - Sept. 2003, April 2005, Oct. 2005, Sept. 2006
Carnival Sensation - September 2007
Last time I checked Verizon Wireless charged $2.49/minute for calls from the ship. Personally I would only make a sea call if it was an emergency. They charge $.69 in PR and San Juan $1.29 in Tortola BVI and other international roaming rates based on where you are going.
RCI Monarch of The Seas 1998
Carnival Miracle 9/24/07
Upcoming Fascination 11/5/09
How about texting? Does it even work and does it cost more or less than calling?
Nevermind, found out for myself...if anybody needs to know about t-mobile on the Carnival Elation, roaming is provided by Cingular and is $4.99 per minute. Text messaging from Mexico to US and vice versa is $0.35 per message.