To route all incoming calls on the LINE Port to the Auto Attendant, set:
Physical Interfaces -> LINE Port -> InboundCallRoute : aa
When the Auto Attendant answers, callers will be prompted to press:
1 to continue this call (ring the OBi phone)
2 to make a new call (make an outgoing call as if using the OBi phone)
3 to enter a callback number (have the Auto Attendant call you back after hanging up)
To allow only authorized callers to make outgoing calls, you may wish to PIN protect the Auto Attendant:
Voice Services -> Auto Attendant -> UsePIN : (checked)
Voice Services -> Auto Attendant -> PIN1 : (must be all digits)
NOTE: Due to a bug in the OBi firmware, you will not be able to enable Do Not Disturb (*78) or Call Forward All (*72) on the PHONE Port and still be able to reach the Auto Attendant from the LINE Port. If either of these features is used, all InboundCallRoute processing stops on the SP1, SP2, and LINE Port trunks, breaking the OBi's ability to use techniques such as reaching the Auto Attendant. Even though correcting the problem is extremely simple, I've been informed by Obihai they will not be fixing this bug.