Ussd on the GRAJ protocol. One fee. 195 countries. Join the protocol.
USSD is the menu system on every GSM handset — the technology behind mobile money for hundreds of millions of people. For a protocol that claims to reach anyone, anywhere, it is not a fallback for a poor connection; in several markets it is the primary way people already transact.
No data connection, no app, no storage, no smartphone. It works on a handset that costs very little and is already in the hand of the operator this protocol most wants to reach.
Sessions are short, menus shallow, input numeric. That forces a flow down to what a transaction genuinely needs, which turns out to be a good discipline for every other interface too.
Anybody who has used mobile money already knows the interaction. Meeting people inside a pattern they use daily beats teaching them a better one.
Not built, and the blocker is commercial rather than technical: USSD requires an arrangement with a telecoms aggregator in each market. That is a contract per country, which is why this is honest about being an intention.