The codes that begin with a star and end with a hash - *170# for MTN mobile
money, and one for nearly every service a Ghanaian bank or network offers.
They matter more here than almost anywhere. USSD needs no data, no smartphone and no app: it runs over the signalling channel that carries a phone call, so it works on the cheapest feature phone in a village with one bar of signal. That is why MoMo reached tens of millions of people while app-based wallets elsewhere did not.
The trade-off is the interface. A USSD menu is a numbered list you navigate blind, it times out, and one wrong digit starts you again. Apps are pleasanter and USSD is what still works when the app will not load.
Learn your codes. When the network is congested and the app spins forever, the USSD menu usually still goes through.