About the only way you can call from the ship is on your cabin phone and the cost is about $9.00 per minute. Same if your family calls you. My daughters husband had a medical emergancy on their honeymoon cruise and my daughter ran up a $500.00 bill and so did we. Unfortunately my son-in-law eventually died and NCL still made her pay the bill. So unless it is an emergancy I would not recommend it. Depending on what ports you visit it may be cheaper to call on shore but be careful that too can become expensive.
Also consider emailing home as that will only be about $1.00 per minute. A daily email from home should suffice.