Features:
* trixbox dashboard
* Asterisk(tm) Open Source PBX
* FreePBX web management tool
* SugarCRM
* Munin (via package manager)
* HUDLite server/admin (via package manager)
* IVRGraph (via package manager)
* phpMyAdmin? (via package manager)
* Webmin (via package manager)
* Automated Attendant
* Blacklists
* Blind Transfer
* Call Detail Records
* Call Forward on Busy
* Call Forward on No Answer
* Call Forward Variable
* Call Monitoring
* Call Parking
* Call Queuing
* Call Recording
* Call Routing (DID & ANI)
* Call Snooping
* Call Transfer
* Call Waiting
* Caller ID
* Caller ID Blocking
* Caller ID on Call Waiting
* Calling Cards
* Conference Bridging
* Dial by Name
* Direct Inward System Access
* Do Not Disturb
* ENUM
* Interactive Directory Listing
* Interactive Voice Response (IVR)
* Local and Remote Call Agents
* Music On Hold
* Overhead Paging
* Remote Call Pickup
* Remote Office Support
* Roaming Extensions
* Route by Caller ID
* Supervised Transfer
* Talk Detection
* Text-to-Speech (via Festival)
* Three-way Calling
* Time and Date
* Transcoding
* Trunking
* VoIP Gateways

Voicemail:
* Visual Indicator for Message Waiting
* Stutter Dialtone for Message Waiting
* Voicemail to email
* Web Voicemail Interface

Computer-Telephony Integration:
* AGI (Asterisk Gateway Interface)
* Graphical Call Manager
* Outbound Call Spooling
* TDMoE (Time Division Multiplex over Ethernet)
* Allows direct connection of Asterisk PBX
* Zero latency
* Uses commodity Ethernet hardware
* Voice-over IP
* Allows for integration of physically separate installations

Codecs:
* ADPCM
* G.711 (A-Law & μ-Law)
* G.722
* G.723.1 (pass through)
* G.726
* G.729 (through purchase of a commercial license)
* GSM
* iLBC
 
Protocols:
* IAX™ (Inter-Asterisk Exchange)
* H.323
* SIP (Session Initiation Protocol)
* MGCP (Media Gateway Control Protocol
* SCCP (Cisco® Skinny®)
* Traditional Telephony Interoperability
* FXS
* FXO
* DTMF support
* PRI Protocols