An airtime top-up is a payment that adds prepaid credit for calls, texts or data to a mobile phone number. Most mobile subscriptions in developing countries are prepaid, so topping up is one of the most frequent small payments people make. Credit was once sold as scratch cards with a code; it is now mostly delivered electronically, with the seller keying in the phone number and the mobile network operator crediting the line within seconds.
Top-ups are sold by shops and agents, through bank apps, by USSD menu, and from a mobile wallet, where they are typically the first and most used service. Sellers earn a discount on the face value. Migrants also buy international top-ups for relatives at home, which works as a small-value remittance. In several markets people have transferred airtime between phones as an informal way of sending value, a practice that helped inspire mobile money.