In October 2019, customers of MTN, Nigeria's largest mobile network, were told about a new price: ₦4 for every 20 seconds spent in a bank's USSD menu. USSD is what answers when you dial a code like 737# and a text menu appears on even the most basic handset. Nigerians had been moving money this way for four years. MTN proposed to bill for it the way telephone networks have always billed, by the clock. Within days the telecom regulator told operators to stop charging customers directly.
The price made sense given what the channel was built to do. USSD and its sibling, SIM Toolkit, come from GSM, the 1990s standard behind most of the world's mobile networks. SIM Toolkit runs small menu programs on the SIM chip. The operator issues that chip, and over-the-air updates reach it only through the operator or parties it authorizes. USSD opens a short live session between the handset and a program on the network, and the network normally decides when that session ends. The standards describe the content as operator-defined. Nothing in them forbids money; they assume that whoever writes the menu also owns the session.
For the first wave of mobile money, the assumption fit, because the operator ran the money service. Safaricom's M-Pesa, launched in Kenya in March 2007, lived in a SIM Toolkit menu and still does. A unified USSD menu, *334#, joined it only in 2020.
Nigeria went another way. GTBank's *737#, which added transfers in 2015, and the many bank copies that followed were menus running inside sessions the banks did not own. Consider a transfer that times out and has to be redialed. The customer has made one payment; the network has hosted two sessions. Both counts are accurate. Under a 20-second meter, the cost of a slow menu would likely fall on the customer and the network, leaving the bank that designed the screens as the one party without a bill, and with little reason to make them quicker.
Regulators took until 2021 to decide which count governs the bill, and years more to settle who collects it. They chose the payment: a flat ₦6.98 per transaction, however many sessions it took, which banks deducted from customers' accounts on the operators' behalf. The banks then fell behind on handing the money over. By the industry's account they owed operators nearly ₦300 billion before clearing the debt in early 2026. Since mid-2025 the fee has come out of customers' prepaid airtime instead, so the price follows the payment while the operator collects it directly.
Kenya ran into the architecture from a different direction. In 2016 its Competition Authority ordered providers to show fees before customers confirm, in SIM Toolkit, USSD and app menus alike. Reports in early 2017 expected Safaricom's USSD changes to arrive before its SIM Toolkit ones, probably because a USSD menu sits on one server while a SIM Toolkit menu sits on millions of separate chips.
Outsiders found their own routes onto the screen. In 2014 Kenyan regulators let Equity Bank pilot a thin SIM, a film laid over a customer's existing chip so the bank's own menu could reach phones on Safaricom's network. By 2017 Safaricom's developer platform offered merchants STK Push, which lets their systems pop a payment prompt onto a customer's phone. The customer still types the PIN into that prompt, inside the operator's channel.
Banks, regulators, a rival chip and thousands of merchants have each won some right to put words on that screen. The session, and the moment within it when someone agrees to pay, remain where the GSM designers left them. Two decades of argument have mostly settled who pays for that arrangement, and who may ask for money through it.