On my last cruise (ten days), I called home everyday from the ship and/or the ports where we stopped and my bill was less than fifty dollars.
I guess that ATT gives you a pretty good deal.
Carnival Liberty New Year's Eve 2007
Liberty of the Seas 5/2008+11/2009
Allure 1/16/ 2011
Vision OTS 2-14-2015
Freedom OTS 3/6/16
Booked -Harmony of the Seas. 12/31/16