FusionPBX doesn't do billing or LCR out of the box, but one guy will sell you closed, proprietary, non-free billing and LCR modules that will integrate nicely into FusionPBX. To help with this, there are a number of places in the free FusionPBX codebase that run things that these non-free apps need. Obviously these are all completely undocumented, until now.
These work by checking for an app named "billing". Specifically, they look for the app_config.php
file in the billing folder. The conditional usually looks like this: