would be a nice solution (especially the SPOT device), EXCEPT for the fact that the coverage area doesn't include the SE Atlantic waters. So, from South Africa
you'd have no coverage until you got off Brazil
somewhere, then it would be fine the rest of the way.
By the way, the coverage map on the SPOT website is a bit deceptive. Here's a better one: http://www.globalstarusa.com/en/content.php?cid=300
satphones work anywhere, but are more expensive.
(ham or marine) also work anywhere and could provide coverage.
There are more expensive satellite-based solutions as well.