Asterisk 1.2.1 is an extremely flexible IP PBX that provides an excellent range of telephony features, with the added benefit of being available for free under the GNU General Public License. IT implementers will find Asterisk to be a good choice for a pilot voice-over-IP rollout—one that can grow as the project grows. However, due to design and management difficulties in larger networks, administrators of such networks should not move forward without at least investigating a third-party support contract.
Open-Source Asterisk PBX Calls for Consideration
Review: IP PBX performs well, but complexity increases as implementation grows.