if you are using trixbox CE 2.3 (soon to be 2.4) you can easily add video support for phones like the Grandstream GXV3000 by following these simple instructions.
1. Log into the system via the console, ssh, or use the config file editor
2. Edit /etc/asterisk/sip.confg (use nano, vi, or config file editor)
3. Add the following lines:
allow=h264
videosupport=yes
4. Save your changes
5. If you are logged in via the console or ssh do: amportal restart
6. If you are using the config file editor, click on the "reload configs" link
You can now place video calls and the system will record video for voicemails. Very cool stuff!