Asterisk (and Digium) are leading suppliers of open -source IP PBX software. The Asterisk software is functional, flexible, and extensible. We found it to be a very good platform for setting up a SIP-based system. Like any VoIP system, it does have some security vulnerabilities in its default configuration, but these can be addressed. You can expect adoption of Asterisk to increase in the future and find its use in more and more enterprises .