The Asterisk PBX supports H.323 via two totally separate channel drivers. You can find more information Asterisk's native H.323 support in /path/to/asterisk/channels/h323/README or you can download a third party driver at http://www.inaccessnetworks.com/projects/asterisk-oh323 Asterisk's native H.323 is supported and maintained by Jeremy McNamara (JerJer in irc). Support for the third party H.323 driver is supplied by inAccessNetworks. If you have trouble with either driver you should direct your debug and comments to the appropriate party, making sure to be specific in exactly which H.323 driver you are running. Please, read all supplied documentation before contacting either party for support. Many issues can be quickly resolved by simply following the instructions that are provided.