Amazingly enough, Asterisk has more features than most traditional PBX systems, which are composed of a large box full of hardware. Hence, the Asterisk mantra of 'it's just software'. The following is only a partial list of the many features included with Asterisk:

Automated Attendant: An automated system for answering incoming calls and routing them based on the caller's responses to voice prompts.

Blacklists: Blacklisting is the ability to easily add numbers to a central database that will prevent calls from the blacklisted phone numbers being processed by the system.

Call Detail Records: The detailed call reports and usage statistics to show an administrator the activity of the phone system.

Call Forward on Busy: This feature automatically forwards a call to another extension if the called extension is busy.

Call Forward on No Answer: This feature automatically forwards a call to another extension if the called extension does not answer.

Call Parking: This feature refers to placing a call into a holding state so that it can be picked up at another extension.

Call Queuing: A system that allows inbound callers to sit in a holding room listening to music on-hold until the next available agent is available to speak to them.

Call Recording: The ability to record inbound or outbound calls to .wav files.

Call Routing: Based on the phone number that was dialed (DID) or the number that was called from (ANI), a call can be routed to a specified extension, group, queue, etc.

Call Transfer: This refers to the ability to transfer an existing call to another extension.

Caller-ID: Caller-ID is used to display the phone number and other available information of the user that is calling into the system.

Conference Bridging: Asterisk has the ability to create conference rooms that multiple people can attend at one time for group meetings.

Interactive Directory Listing: A Company directory system that can look up users by first or last name.

Interactive Voice Response (IVR): This system uses pre-recorded voice menus to prompt callers to make selections via their phone such as "press 1 for sales, 2 for support".

Music On-Hold: Asterisk can play MP3 files to callers who are on-hold or waiting in a queue.

Remote Office Support: Asterisk uses Internet Protocols for communication. Hence, users can be at remote locations and have access to the system via broadband Internet connection.

VoIP Gateways: Using the new Internet Telephone Service Providers (ITSPs), an Asterisk system can have telephone network connectivity without having to use a normal analog service provider.

Voicemail: Each user in an Asterisk system can have their extension and voicemail account. Using TrixBox, the voicemail can be retrieved via their phone, from a remote location, sent via email, or accessed via a web browser.

At the time of writing, Asterisk was at version 1.2 branch. Some of the new features in this version include:

A new dynamic IVR (Interactive Voice Response) flow-control interface

PRI improvement

SIP support improvements

Customized CDR (Call Detail Record) support

A real-time database configuration storage engine

A new real-time interface that allows for faster and less disruptive configuration changes

New dial plan syntax and a new dial plan language, including many new applications and dial plan functions

Improvements in protocol handling for better voice quality