If you are a contract subscriber on the Vodacom network, then checking to see how many free minutes you have is particularly easy thanks to the 111 USSD service Vodacom has in place.
To use, dial *111#. From the resulting menu, select 1 for balances. From the next menu, select 1 again, thereby choosing the “Free Minute Balance” menu option.
Simple as that really.
(From what I understand, this service is completely free of charge. How nice of them.)