The numbers tell the story: There are roughly 40 million users of mobile payments systems worldwide. About half are residents of Sub-Saharan Africa who use a system developed in Kenya that last year processed an average of $500-million of transactions a month.

In fact, the Kenyan system known as M-PESA has become so successful that it now accounts for a meaningful chunk of the national economy.

Trouble is, the Kenyans may be too successful. The World Bank is warning that the handful of companies dominating the industry in the African country may have become too big for the good of the global mobile payments industry, amassing potentially monopolistic clout to the detriment of their competitors in other countries.