Yes, we have done it quite a few times. You can only do it when you are either in port or very close to port. We have Sprint, and at the time, we did not have an international plan. We didn't have blackberry's, iphones, or anything, just plain phones. What happens is that it uses the ships satellite to be able to make the call. The best thing to do is contact your phone company, tell them where you'll be and see what the rates are.
I think when we were calling from GC or Cozumel (can't remember which one) it was a couple dollars a minute. But for us, business owners, it was a deal. Dealing with phone cards can be a pain, the ship is $7 a minute, etc etc.
One thing we did to keep in touch was to use the internet plan. We'd type the message on our computer first, and then just use a few minutes to cut and paste into the document we were sending. We'd hurry and check our inbox, and would be done.