device and user mode is a freepbx invention/hack. It is not a fop2 feature. If you set your freepbx to use user and device mode, the only thing that matters is the extension, not the device. So if you have 3 real persons or 10, you are not going to know who they are. You just know that extension XXXX is reachable or not.
You can see which device an extension is using by querying the astdb for it, I do not remember exactly the family, but it should be easy to search for it.
Best regards,
