Look - I think VoIP is a thing of the future. I also think that it will erode margins. However - I do believe that there are ways to go about it. I quite successfully use skype on my 3G contract via my laptop.
I don't understand what they try to do however. If they were smart they would have tried to corner a niche business market with higher margins. Instead they launched a customer service. Seriously - if these guys fail, they can not blame the networks.
MXit is quite a different application to SMS - so it doesn't make sense to draw a direct comparison. But if you want to you can immediately say that MXiT is unreliable as hell (outages are VERY common) and even for text they already struggle with growing infrastructure organically. Voice is 10 times more difficult to do than text. And it is going to be at least 30 times more expensive.
MXiT has the advantage that its a craze among school kids. And it runs on plain vanilla J2ME. This VoIP solution requires Symbian or Windows Mobile. Did these guys actually determine the percentage of people with Symbian phones? Did they do market research on how many people will base their handset decision on such a service? Have they actually seen what horrible response NMP got? Do they have any idea what it cost to develop and maintain mobile software (I did a bunch of Symbian programming for more than two years). Applications need to be signed. Applications can be locked out on a network's request (Due to "stability" issues).
I cheesed because these guys will end up making the networks stronger. And they will complain about failure for reasons other than their own incapability to do market research. I suggest they re-evaluate their business plan. I'm sure with their IP and skills, they can do a lot better with a slightly different product.
UPDATE:
Apparently I'm wrong. These guys are actually bluevoice.co.za. A winner of the enabilis (
http://www.enablis.org/competition/winners/) competition. They also had lots of support from various companies it seems. Maybe it will work. Who am I to critique FNB, Microsoft etc. The mobile networks will roll over and die! I'm going to punish myself now.
NOT.