With the callback procedure, the TC provider switches a low-cost or free connection via a callback. To activate the service, the caller dials one phone number of the provider and allows the connection to be established for one or more rings before hanging up. The provider has identified the caller's phone number from the call, calls the identified number and provides a cost-effective connection. The caller can now enter the complete phone number and set up the desired connection.
A similar variant to Callback is call through.