I use Trixbox a lot at work, and found trixboxgraph really useful for seeing what the dialplan is on the system. I've taken a bit of time and modified the code to do a couple of things it didn't before, and hopefully, make it a bit easier to configure the look of the resulting images.
As a comparison, here is the output for a fairly simple dialplan using the original code, and the same dialplan with my version.

• Trixbox 2.6 (Tested on 2.6.1)
  • index - View
  • functions.php - View
  • settings.php - View
  • styles.css - View
• Trixbox 2.4 index.php - View
• Trixbox 2.2 index.php - View
• functions.php - View
• settings.php - View

Trixboxgraph was installed via ssh using yum install tb-trixboxgraph (or yum install trixboxGraph on Trixbox 2.2 & 2.4)
To prevent /var/log/httpd/error_log filling up with "Error: Could not find/open font", I copied arial.ttf to /usr/share/fonts/truetype
I've tried this on Trixbox 2.2 (vmware), Trixbox 2.4, Trixbox 2.6.0.7 and Trixbox 2.6.1 (vmware). All you need to do is copy the files to /var/www/html/tb-trixboxgraph (or /var/www/html/trixboxGraph)