If she's non-African, she will be beseiged from the moment she steps off the plane with people trying to sell her stuff. (If she's African, same thing if she's wearing western clothes and generally looks like a visitor). Phone cards etc will be one of the many items on offer.

What she needs to ask for first is a 'starter pack'. This will include a SIM with a local number, and a certain amount of air time credit. After that she needs recharge packets which have no SIM, just credit. Any shop based seller (as opposed to street tout) will have starter packs.

The SIM just goes in the phone and starts working (it is an unlocked phone, isn't it ?). The air time cards have a scratch-off area on the back. This reveals a 16 digit number, which is keyed into the phone along with a network sequence. The network sequence is usually printed on the card. So something like *23456*<16 digit code># <send>, and you should get an immediate ack that the code has been recvd and the phone has been credited.

As you've already identified, by far the cheapest usage is to have someone call her from abroad.

Regards

Mark