I have heard that making phones calls can become expensive, we plan on purchasing calling cards to call home, not sure how they calculate the minutes from the western carb area the trip is 5 days - how many minutes should I purchase and will they work at the distance we are going?. This is our first cruise and away for the first time from our children (they are young in age) want to touch base with the homestead regarding them.
There should be an internet cafe on your ship. You might want to consider sending e-mails daily to the people taking care of your kids and calling when needed. A hotmail or yahoo account can be set up in seconds if the people taking care of your kids don't have an existing account.
I know the AT&T calling cards at Sam's Club have a minutes conversion table on them for popular countries and then a number to call to get minute conversions for countries not listed on the card. Mexico has a really bad minutes exchange rate with most calling cards and that is almost impossible to find a phone that you can actually use the cards with. There is an international calling center between where the ship docks and the downtown in Cozumel that might be a better option then trapsing around trying to find a phone that the card works with.
Something that people do is just use their cell phones. It might be cheaper to pay the roaming fee, depending on your phone then to use a calling card and definately cheaper then using the ship's phone ($6.99/minute).