If there of no line they charge you for a bunch of useless things like installation fees, once off fee and 1 time connect which wil cost something like R1200 or you can get the telkom simple and everything is free.
They will give you preference if you fix date a transfer of your existing telephone line.
You need to give them at least 3 weeks notice .
Fixed dating the transfer will make sure they put the phone in on the fixed date .
And the transfer is not free AFIK .
Best of luck you going to need it .
even if you give them notice they wipe your ass off on you and do their own thing.
If you don't use the line for phone calls (or getting phone calls) then it's best to cancel your current one and order a new line. Take a Closer package that includes the installation costs for free and then cancel it after a month to save money