It is a call which is made over internet protocol (VoIP). For example,
one can call using Google Voice to other recipient located miles away. Such
call can also be international.
Main portion of the advantages of the Asterisk server appears from it being an open source downloadable product. Most of the users, especially business people, can find it difficult to understand the idea behind this principle, or free software, but a business models behind open source are different and specific, as in case with Asterisk server.