To setup an ObiHai adapter to behave as a Ring-down device (automatically dial a number when the phone is taken off-hook), a single modification to the dialplan is required.
In the web GUI:
Physical Interfaces \ Phone Port 1
Change the "DigitMap" to the following, where #num is the number you wish to dial.
So, to dial the extension 1001, you would use: (<1001>)
Since this is a custom setting that overwrites the standard digitmap, you will likely need to remove the device from auto-provisioning to ensure the setting is not reverted.