A call center is a centralized office used for processing (receiving and transmitting) a large number of data and telephone calls.
Call center is extremely suitable for the telecommunication marketing. Basic functions of a call center are:

Receiving inbound calls – requests for delivery and reservations, catalogue sales, trade information, technical support for customers Outbound calls – providing marketing surveys, promotional campaign effectiveness assessments , debt collection, interest evaluations, event management. Some companies and institutions (for instance banks) where employees receive and process great number of  calls every day. set up their own call centers.

A new term becomes popular in the call center theory . This term is a "Contact center". It is a call center, where except phone calls, numerous letters, faxes, SMS, e-mails can be handled.
Call centers usually provide comfortable and spacious workstations for their agents. Workstations are equipped with a PC, stationary or a software telephone (headset), connected to a telephone service  provider  (telecom) and to the corporate computer network.
Most of the companies use call centers to interact with their customers. Such are  utility companies, insurance companies, pharmaceutical companies, customer hardware and software support. Some companies use call centers for internal use, like help desk and after-sales support.   
Infoserv^® systems are suitable for both large and medium sized companies and for small firms.  Minor business organizations can turn InfoServ^® Customer manager into a powerful tool for increasing their competitive capacity and cover a bigger market share.