The B&O phone doesn't seem to have a whole load of technical info available about it online. Only useful information seems to be to make sure you are plugged into L1/L2 socket on the base for a single line and that the handset is correctly paired with the base.
When you are connecting the B&O base to the VM hub, are you using a lead from the B&O base which has a normal BT plug on the end of it which you are then plugging into the VM-supplied adapter (BT socket to RJ11 plug)?
Or are you trying to connect the B&O base with a RJ11 lead/plug straight into the back of the hub without the VM-supplied adapter?
If you do have a working line but using a different phone, then you would probably do best to contact B&O support direct esp. since the device seems to be quite old and not that well documented online.