Asterisk PBX (private branch exchange) is an open source telephone system. Like any PBX, it allows a number of attached telephones to make calls to one another, and to connect to other telephone services including the public switched telephone network (PSTN).
Setting up Asterisk is considered as a difficult task. Building a VoIP Linux server with Asterisk is easy with AsteriskNOW software, which can setup Asterisk in minutes:
AsteriskNOW is an open source Software Appliance; a customized Linux distribution that includes Asterisk (the leading open source telephony engine and tool kit), the AsteriskGUI, and all other software needed for an Asterisk system. AsteriskNOW is easy to install, and offers flexibility, functionality and features not available in advanced, high-cost proprietary business systems.
Overall I'm quite impressed with this project as it provides:
=> Ease of use
=> Ease of installation
=> GUI Wizards
=> Open source project
==> Visit official AsteriskNow project home page.