Hi Judy. If you are still a Solo Mobile customer, your phone is probably a CDMA phone. This technology is not well used outside of North America (and no longer in North America for that matter). As such, Solo never offered any international roaming packages.

You might be best served buying an inexpensive unlocked phone for travelling (like this one). Or....any quad-band GSM phone (iPhone, Motorola G4, etc.). 

There are several advantages of an unlocked phone. But in your case, having a unlocked smartphone will allow you to buy a local SIM card in Africa and activate a prepaid plan. This will almost certainly be far cheaper than any roaming plan you could purchase back at home with your local carrier.

The downside here? You can't keep your number. You'll have a Africa local number while travelling.