Many VoIP providers use Asterisk. Why? Because Asterisk is a free, open source program that allows you to build an IP PBX out of any computer.

Very often, VoIP providers use Asterisk to supply their hosted PBX service and many VoIP service providers that don't use Asterisk often offer service that is compatible with Asterisk on the user's end.

• CallCentric
• MasterDigital
• nexVortex
• Telasip
• Teledynamic Communications
• Teliax
• TelTub
• ThinkBright
• TinCanTalk
• ZingoTel

Many VoIP providers will be compatible with Asterisk (many more than just these ones), but call and ask to make sure your service can use Asterisk if they don't specify anywhere else.

Asterisk is an open source communications server. Asterisk can be configured to create an IP PBX, hybrid PBX, call center, or routing manager.

For small to medium-sized businesses, Asterisk is a powerful platform to manage telecommunications. Developed by Digium, Asterisk can turn any computer into a telecom server. Asterisk is compatible with Linux, Unix-based OS and OSX.

Asterisk can work with a hardware PBX, but no additional hardware is necessary to run Asterisk.

The software has a native protocol, IAX, but Asterisk can also run with the SIP and H.323 protocols.

While Asterisk is primarily designed for a business PBX, the software can definitely be configured for home VoIP service. A tech-savvy home user can set up Asterisk in just a few hours.

A basic VoIP provider and an Asterisk server can help you save on your phone bill - service, in general, is cheaper with a VoIP service provider. Asterisk allows you to set up complex routing rules for calls to your home phone and Asterisk can allow you to set up your own home office. Of course, you do need to have a computer that is constantly on in order to use Asterisk at home. (When you turn off that computer, so does your phone system). A computer designed specifically to run Asterisk is called an Asterisk appliance.

Configuration of Asterisk is not the simplest process but it is a free alternative to very complicated configurations of IP PBX with hardware and networking equipment. Digium now offers online training for a small fee.

Asterisk offers all the features a VoIP provider offers with a hosted PBX.

Standard features include:

• call waiting
• voicemail
• call transfer
• caller ID
• conference calling
• interactive voice response
• music on hold

Additional features include (non-exhaustive list):

• call forward on busy, on no answer
• call monitoring
• call queuing
• E911
• fax
• remote call pickup
• SMS messaging (short message service, aka texts)
• voicemail to email
• web voicemail interface

In addition to IAX, SIP, and H.323 protocols, Asterisk supports:

• Google Talk
• Jingle/XMPP
• MGCP
• SCCP
• Skype
• UNIStim

Asterisk's open source status allows for expansion, innovation, and flexibility. For example, in 2006, Digium incorporated Google Talk into Asterisk servers, so that calls to Asterisk can be forwarded to Google Talk clients.

Other protocols for PSTN lines are compatible, but you will probably need some kind of hardware converter to make calls using your PSTN line and your Asterisk server.