Some companies will use dialling systems to make sure their agents are taking as many phone calls as possible. These systems will predict when the next agent will be available to take a call and then place an outbound call in anticipation of the agent freeing up on time. This ensures a constant flow of calls to the agents. There are currently several dialler options available in both open-source and commercial-product offerings.
In open-source there is ViciDial (http://astguiclient.sourceforge.net/vicidial.html) and GnuDialer (http://www.gnudialer.org), and in commercial-product offerings we have SineDialer (http://sineapps.com).