Nexus ISP http://www.nexus.co.za/voip.html will give you a free 021 number, signup send them the required proof that you live in the area and you get a free number. You only get billed if you make outbound calls on it.
Has anybody tried this from outside South Africa? I don't see anything in the T&C about this service being limited to being based in SA only. I still have a South African ID number, am a South African citizen. Just living in NZ now but have to enter a SA address. Any advice?