The Obi isn't forwarding the call. The Obi receives the call from your cell and then makes a new call using your land line, and bridges the 2 calls together. Since the call is new it carries the caller id of the origin (land line).
There is no way to spoof the caller id on your land line. You can block it.
You can have the Obi fork the calls coming in on your landline to your cell. Of course the customer already has your home number. And again a caller id problem (the caller id coming in on your cell with the forked calls is that of the Obi, not the actual call).