I'm looking at normal phone calls mainly. Iridium looks good because of the coverage, but then the other networks offer enough coverage for my purposes so Thuraya or Inmarsat would also seemingly do the job.

I just want something easy and stable so my parents can call at the $1-1.50 rate without resorting to crazy roaming charges that some GSM networks can employ. Plus with lots of time spend at open seas it seems a satphone would be ideal.