This is a process of connection between a computer and an ordinary phone. For example, one can call from Skype to a cell phone by dialing a specific number.
In order to take care of the billing process and keep track of calls it is essential to have some sort of computer software. The system you are planning to select should allow the manager setting up prices per minutes and show the reports of calls that were made by the customers. For the operator the installed software has to provide a possibility to control the booth status, what amount to charge and generate invoices or receipts.