Have you done a factory reset? If yes, proceed.
Unplug the ethernet cable. Ensure the phone is plugged in directly to the OBi - not through house wiring, not through a fax machine etc. And the phone must tone dial.
Take the phone off-hook and listen. Do you hear dial tone?
Dial ***1. Do you hear a voice? (It is generated inside the OBi.)
If your answer to any of the last two questions is 'no', then either the OBi or the phone is defective.