Could you just text your parents on the ship and ask them to call at next port? I have AT&T. I was able to receive texts for free (I think, my company pays the bill) on the ships GSM network. I did not send any so I have no idea what they cost. I also received multiple phone calls, but I did not answer any of them. My family has a 3 call rule. If someone calls 3 times in a row (within 5min or so) than it's an emergency. Note: Nice feature on the iPhone allows 3 calls in 5 minutes to ring through regardless of vibrate setting.

Sat phones sound cool, but it's a high up front expense (and monthly) and not that easy to use unless you have a clear view of the sky.

For just crusing, you'd have to really talk a lot to have an ROI better than a simple GSM phone...

No government (or really anyone else) is your friend when it comes to privacy!