Rica a Telkom prepaid sim, then follow the sms port options. Easy, takes anything from a few hours to 30+. Do it around 5-6pm and should be done by 11pm.
To clarify:
SMS from your CURRENT phone ( ICCIC number is on the TELKOM sim card you want to PORT TO )
You will get a confirmation message on your CURRENT SIM. MTN was just a notice, no confirmation but dunno about Cell C.
Once your current sim dies, plug in your new sim and away you go.
Also note that you start on the Move prepaid plan. I changed the wife and I to the Sim-Sonke one and buy the free-me bundle. Worked great for us this last month, R20 airtime + R69 bundle, still got lots left.
Obviously ensure the sim is rica'ed first!