A call center is a common interface between a commercial interest and its customers.  A toll-free telephone number is often provided to customers as a source of such services as product information and technical support.  Agents are hired to receive incoming calls and provide the customers that call the toll-free telephone number with a service.  Call centers may also be a source of outbound calls.  Agents place calls which may, for instance, follow-up the provision of a service, announce new products, schedule a delivery or canvass donations. 
Often, the pool of agents is subdivided into sets of agents according to common skills, i.e. language proficiency, possessed by each agent.  For instance, a pool of agents may be divided into skill-sets for proficiency in English, French and German.  Understandably, some agents may be part of more than one skill-set. 
An inbound call at a call center may be directed to an agent in a particular skill-set based on information supplied by a caller.  For example, a needed skill-set may be determined through answers to voice response questions.  Information about a caller may already be held in a customer database, populated by information received on a product registration form or in previous dealings with the customer and this information may be used instead of, or as well as, information learned via voice response answers. 
A blended call center uses one pool of agents as a source of outbound calls and as a resource for receiving inbound calls.  It is in the best interest of a call center administrator to minimize waiting time, that is, the length of time a customer spends on hold, waiting for an agent.  It is also in the best interest of the call center administrator to minimize the number of paid agents and maximize their use.  Unfortunately, these interests are at odds with one another.  If all agents are busy either receiving or placing calls, none are available to receive the next inbound call.  If all agents are available to receive calls, then they are not being used efficiently.  Thus, a balance must be struck.