Im on MTN Off-peak top-up and im able to load data bundles now, *141*6# method..thou i did get some error msgs at times, i myself im getting to know how this works. Guys at an MTN store refused to believe that i can do that. Well never-mind them you can, i did.
I also got a weekend everyday contact with Vodacom and I must say they fast, billing and other activation of contact was great. You get a safer feeling taking up a contract with Vodacom than MTN i feel. MTN doesnt have its own "own" SP far as i know if you taking up a contract with MTN in an MTN store your s.p is some mobile connection company. With Vodacom, Vodacom is your SP,the company itself. It took me 3 days to get my top-up contract , and 15min for my Vodacom contract to get going.