This is a process of connection between a computer and an ordinary phone. For example, one can call from Skype to a cell phone by dialing a specific number.
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.