Mxit was just dodgy, stupid rooms, and you kept having to pay for dumb ass stuff. Honestly it sucked. With tripadvisor it was fine. Design a simple chat interface without any complications for the users. allow to send small files and images, let alone songs of certain sizes, and that was that. Dont add rooms, or gimmicks etc. Let the users design their own groups, and have no involvement in who they add, or how it looks, or how it's controlled. Also basically dont charge anyone for using the service.
Thats how tripadvisor partly started too. They started with another plan, and then bought out one of my review sites, and integrated it fully. The review site was started when I was asked to tip an irritating waiter after waiting for 2 hours for a steak. Really awful service, but they kept demanding I tip. So got grumpy and built a review site with one review. When it was sold and integrated for them, it had over 1 million reviews of restaurants world-wide. The idea, create a simply website where users can fill in their own details if it doesnt exist, and put in restaurant details. Anyone could then review it, but would be blocked from using swear words etc. I didnt have to control it. I attached it to yahoo back then, and it just worked. It made me a pretty penny and some shares.