The fundamental problem with all payment systems is to accurately verify the identification of the buyer. If one can be hundred percent sure that the identification of the buyer is absolutely accurate, one can be hundred percent sure that the payment is not fraudulent. In the physical world this is achieved by verifying physical documentation (for instance ID documents, fingerprints etc.). The problem is of course much more difficult in the digital world.
That is why solving digital identification is almost the same as building a fraud-proof digital payment system. This is emphasised by a recent announcement from Paypal (Read here). In this announcement, Paypal aims to become the custodian for their clients' digital ID's. Similarly, deploying well-designed mobile payment solutions in emerging markets is similar to rolling out robust identification systems. One should consider combining both problems: rolling our national ID systems at the same time as deploying mobile payment systems.