Short codes (also known as short numbers) are special telephone numbers, significantly shorter than full telephone numbers, that can be used to address SMS and MMS messages from certain service provider's mobile phones or fixed phones. There are two types of short codes: dialing and messaging.
Short codes are designed to be easier to read and remember than normal telephone numbers. Like telephone numbers, short codes are unique to each operator at the technological level. Even so, providers generally have agreements to avoid overlaps. In some countries, such as the United States, some classes of numbers are inter-operator (U.S. inter-operator numbers are called common short codes).
Short codes are widely used for value-added services such as television program voting, ordering ringtones, charity donations and mobile services. Messages sent to a short code can be billed at a higher rate than a standard SMS and may even subscribe a customer to a recurring monthly service that will be added to the customer's mobile phone bill until the user texts, for example, the word "STOP" to terminate the service.