Like a telkom one. You can transfer your number from one provider (telkom) to another (neotel) so you wont neccesarily be able to tell what network you are calling just by the number
Found this thread on google search. I know numbers can be ported, so you can't be sure, but new numbers seem to start with a 0 after the dialling code. Like 011 018 etc. I see a lot of government departments using these numbers now... Can anyone confirm the 0?