I live in the USA (Atlanta) and my son lives in Pretoria. We would like to play together. Can he play Starcraft 2 on the US server(s) with me? How does he go about it?
Nope. In the beta I got put in US region and I had to email Blizzard to change it which took about a week... Im not sure they will allow this with the official version though.
My recommendation is that your son buys the extra copy for you knersus as the cd-key is region bound so you can have both the US and EU version on your bnet account but then you must also realise that you will have to have the EU client installed as well.
I suggest that you should both play on the EU server because the ping from SA to US is horrible but I THINK the ping from US to EU would be better...
ping jolt.co.uk to check.