Phone calls on the ship can be expensive (although believe it or not the prices I'm about to quote have come down from previous highs). They will cost you roughly $9.95 per minute (varies by a dollar or so from line to line).
Internet costs aboard ship also depend on what line. Figure 75 cents to a dollar a minute, but packages of minutes and unlimited use packages can be purchased that lower the per minute cost greatly. Stll expensive however.
In most ports you can find very inexpensive internet cafes and kiosks that get cost down as low as 3 dollars for a half hour. Ask your waiters and stewards. Crew use these locations all the time and will know where the cheaper ones are located.