Default dial plan
The default dial plan that is provided with FusionPBX is a modified version of the FreeSwitch default dial plan. The modification is that all the pre-defined features in FreeSwitch have been prefixed with * to free up number ranges to enable FusionPBX to support extensions of 3-6 digits in length without conflicting with any pre-defined features.
You can modify the advanced dialplan if you want to change the way it operates. If you do, note that everything before
<X-PRE-PROCESS cmd="include" data="default/*.xml"/>
is executed in the dial plan BEFORE the dial plan entries you set in the dial plan manager (Dialplan-Dialplan Manager) and everything after that line is executed AFTER the dial plan entries you set in the dial plan manager.
One possible change you might want to do can be found in the Apps-IVR Menu wiki entry. It affects what happens when you transfer a call - should the caller hear music on hold or ringing sounds.