Asterisk: The software phone company
Asterisk is a phone system in software. It can replace large and expensive business phone systems, powering thousands of extensions, or it can help home users save money on long distance. Because it’s implemented in software, it is extremely versatile, easy to customize, and easy to extend.
You’re probably familiar with the concept of a Private Branch Exchange (PBX) already, though you might not know it. Almost every medium or large business has one. A PBX is, basically, a simplified version of a telephone company’s exchange. If you’re accustomed to dialing 9 to place an outside call, or dialing a simple 3- or 4-digit number to reach another extension, you’re using a PBX.
Asterisk is different for several reasons. The most important is that it’s an all-software approach. Instead of switching analog lines in hardware, it routes and manipulates Voice Over Internet Protocol (VoIP) packets in software.