Like many people today, I've switched to VOIP to get more features for my phone system for less cost.  I configured Trixbox and run it as a virtualized Xen HVM domU, to be precise.

One thing I have struggled with was getting an Enum trunk to work properly.  An Enum trunk will do a lookup on e164.org, and if the number is found in the database, a VOIP-VOIP call can be made, which bypasses using minutes with your VOIP provider(s).  I searched the trixbox forums, and found this fix:

Go to /var/www/admin/modules/core/agi-bin/enumlookup.agi, and edit line 61 from:

$dialstr .= $nextURI[$URI]."|";

to:

$dialstr .= $nextURI[$URI]."%";

This fixed the problem for me.  You may also need to edit /var/lib/asterisk/agi-bin/enumlookup.agi and edit the same line. The tutorials say that editing the first file mentioned above will overwrite the second, but I edited both to be sure, and then restarted Asterisk.

The place in the Trixbox forums I found this solution was:

http://www.trixbox.org/forums/trixbox-ce-development-forum/beta-forum/enum-woes