M-Pesa is the world’s most successful mobile money service. It enables users to send and receive money, top-up airtime and make bill payments through their mobile phones.
Customers register for the service at an authorized agent. To get electronic money onto their phones, the user visits a cash-in/cash-out agent and deposits physical cash in exchange for electronic money which they can send to their family or friends. All transactions are authenticated by entering a PIN number and both parties receive an SMS confirmation of amounts transferred. All transactions happen in real time. E-money can also be exchanged for physical cash by visiting an agent and making a withdrawal.
For an overview and history of M-PESA check out this explainer.