US Postal Service money orders can be purchased with cash and used the same way as a certified check. This works for utility payments. Mobile phone companies take cash as payments, in both their dedicated retail stores and a large network of affiliated airtime merchants. In some countries, there's a mini-economy for the trade of airtime minutes within cellphone networks, based on physical stores that can convert cash->minutes. M-Pesa was one of the earlier success stories, unifying payments and digital identity, but it was anchored in real-world ingress points for cash.

Cash & digital can be complementary.