We've used them on a few cruises but don't bother anymore. We never got good reception for more than a couple decks of separation, so it ended up being more of a hassle than anything else. I've also seen a decline in usage on our past couple of cruises, so perhaps this fad is fading away.
Right, it was like doing a Verizon commercial. I also hate carrying a lot of junk around with me on the ship. If I can get by with just the cruise card and sunglasses, then that is my preference.
If the ship you're going on has satellite phone service the cheapest & simplest way to communicate is to text message each other. I don't know what the cost would be.
Be careful, some providers and plans will charge roaming fees. If you use the ships tower satellite) and not an inside network tower for access there may be substantial cost involved. Check with your provider before assuming its low cost.