It is a device capturing and controling all the signals, which are being created by the whole system, especially the made and received phone call signals. The device is mostly used for connecting regular phone system with the Internet and backwards.
For one time advertising promotions or typical requests it is easier to use services of the outsourced call center. Main advantage of such a service is that the company who rents it is free from the necessity of keeping the operators and organizing their work flow.