If you have your Obi in an Obitalk account you can access it from there using the Expert Configuration.
In order to use an Obi for a default gateway for a softphone number, the Obi must be listed in the account for that softphone number. You cannot jsut add a second softphone number to the Obi as it's default gateway in a conventional manner. You can add it to the circle of trust of the Obi and access the services through the Auto Attendant.
To use the same Obi as a default gateway for multiple softphone numbers see this thread.
http://www.obitalk.com/forum/index.php?topic=3550.0