I think the spectrum auction is a bit unfair. Only those with deep pockets will bag some spectrum which not really mean that prices will go down. In fact prices might even stay the same just the average speeds will likely increase.
Quickest way to lower prices in a market? Just have someone that is gaining market share through lower cost products like Capitec or Afrihost. You cant expect MTN or VC to do it for fun, only if Cell C/telkom/rain managed would it happen. Actually VC and MTN might need to reduce prices some time because I suspect that many previous subscribers have already bypassed/reduced usage of data from them by using fibre plus whatsapp.