A contact center is a centralized office used for the purpose of sending & receiving large volumes of requests by telephone.

A contact center is operated by a company to administer incoming product support or information inquiries from consumers. Outgoing calls for telemarketing, clientèle, and debt collection are also made. In addition to a call center, collective handling of letters, faxes, and e-mails at one location is known as a contact center.
A contact center is often operated through an extensive open workspace for call center agents, with work stations that include a computer for each agent, a telephone set/headset connected to a telecom switch, and one or more supervisor stations. It can be independently operated or networked with additional centers, often linked to a corporate computer network, including mainframes, microcomputers and LANs. Increasingly, the voice and data pathways into the center are linked through a set of new technologies called computer telephony integration (CTI).

Most major businesses use call centers to interact with their customers. Examples include utility companies, mail order catalogue firms, and customer support for computer hardware and software. Some businesses even service internal functions through call centers. Examples of this include help desks and sales support. However, some companies employ staff to work in their call centers almost by "bulk", applicants requiring little or no educational qualifications or experience; an example is Lloyds TSB. In contrast, some firms demand lengthy customer service experience, various formal certificates and impose a complicated and staged recruitment interview procedure; an example of this is American Express. - Wikipedia

Mathematics

A call center can be viewed, from an operational point of view, as a queuing network. The simplest call center, consisting of a single type of customers and statistically-identical servers, can be viewed as a single-queue. Queuing theory is a branch of mathematics in which models of such queuing systems have been developed. These models, in turn, are used to support work force planning and management, for example by helping answer the following common staffing-question: given a service-level, as determined by management, what is the least number of telephone agents that is required to achieve it. (Prevalent examples of service levels are: at least 80% of the callers are answered within 20 seconds; or, no more than 3% of the customers’ hang-up, due to their impatience, before being served. ...