Steve,
I travel a lot to Mozambique and I can tell you that I almost exclusively use Skype (PC to PC) for contacts with my HQ and my family. It all depends on the available Internet connection: if you end up with a 56k modem line, you may face some "noise" but you can keep an understandable conversation. With some form of broadband Internet connection, conversations have the same quality of International mobile phone.
I hope this helps you.
Regards.