When you go operational you get the Operational Welfare package which includes Paradigm cards. These are 'phone cards' that get credited with 10/20 minutes worth of phone calls every sunday. You then queue up to get onto the specific phones around the ship that can 'phone out' via sat coms.
on my 1st deployment i did not call/write home for months - it is the reason you join up. a bit like the French foreign legion, but not as hard and you don't need to change your name. a bit more fun as well!!