is there Sat phone coverage in South Africa?

Irridium yes, but not Thuria. However, most of RSA has reasonably good cell phone coverage, so you don't really need a sat phone.

My AT&T cell phone worked better in RSA and most of Namibia than it does in Florida.

How about buying a cheap cell phone when you arrive in RSA at the airport? That way get it on a pay an go tariff, when you leave give it to one of the trackers as part of their tip.