Thanks for the confirmation on the Sams club card - our experience was the exact same as yours on Grand Cayman & Cozumel. I didn't think we were that stupid that we just couldn't figure out how to work it on the islands. :~)
Also, thanks for all the info on how to make a call from those places. I wish (& my daughter especially wishes) we had known all that before we went. Oh well, next time we'll do better. And there's always a next time for a cruise, right?