I use the telkom line as an incoming line but most of my calls go out over VOIP to switchtel and then they break out via the cheapest route. The telkom line works very well, my only problem is I can only do one incoming call on it without voip or my premicell for extra incoming channels.
My main client (Men's Clinic International) has 3 adsl modems in Parkmore, JHB that each pay for a voice line that is never used. Each modem is on the highest speed (4MB?) because we need all the UPLOAD speed we can get.