Obi + [GV or other SIP) = OOMA
If there are reliable internet connection in South Africa, you may consider deploy an Obi110 over there. You will call South Africa through this path:
Obi(US) -> Obi110(Africa) -> phone
Obi(US) -> Obi110(Africa) -> PSTN -> some one's phone.
OBi to OBi is completely free. You can direct dial an OBi device with its unique nine-digit number.