Yes, that's right – you can now set your NoPBX number(s) to automatically call back your users, when they make a call in to that number.  The beauty of it is, the user does not need to have the NoPBX app running on their phone – the PBX identifies them from their CLi (note that their SIM does need to present CLi when calling).

Why would you want this?  Well, it solves a few use cases:

1) For users with old phones, who are not able to run the NoPBX app – now they can get connected to the office free, just by dialling the call-back number.

2) For companies like couriers, who eg. want their drivers to be able to call the office free of charge without giving them airtime or the full NoPBX app.

3) Using a dedicated call-back number to provide in-house users with direct inward access to a specific ring group or extension, such as a technical support desk.