Thank you for your suggestions. I think I have a workable solution. Here's what I found:
Quote from: QBZappy on April 23, 2013, 07:47:53 PM
Physical Interfaces
PHONE Port
LINE Port->CallForwardUnconditionalEnable
->CallForwardUnconditionalNumber (GV number)
This did not work for me. An incoming caller did not go to voicemail (other GV account), and did not notice any difference from before the setting was made. Note that an exclamation mark had appeared beside both the 'enable' box and the number I typed as soon as I 'submitted' the change.
Quote from: giqcass on April 23, 2013, 07:43:52 PM
You would need to test this but I think you could put this in the incoming dial plan under physical devices for you phone line. {SP1(xxxxxxxxxx)}
You would need a service provider set up for SP1 for this to work. If you use Google Voice as a service provider it shouldn't be the same Google Voice account that you are trying to call or you will have problems. If you have a service provider in slot SP2 then replace SP1 with SP2.
This worked. The appropriate field is actually called InboundCallRoute, and contained 'ph' before I changed it to {SP1(xxxxxxxxxx)}; after changing, it also had an exclamation mark beside it, but forwarding worked anyway. I followed the advice about using a different GV number. When someone calls my home landline, it rings the phone attached to the Obi twice then the phone enunciates the caller's name/number (a Panasonic feature), then goes silent. The caller hears two rings then gets the GV account voicemail. I believe that while the house phone is ringing someone in the house can pick up and talk to the caller. This might be fine, in my case I would unplug the house phones or turn off their ringers so my friend is not disturbed. I could say this is a workable solution.
You are supposed to be able to enable call unconditional call forwarding using a star code (*72) on the attached phone, but when I try it I get a continuous tone (even though some of the other star codes seem to work).
I found the following paragraph about this in the OBiDeviceAdminGuide.pdf, but I don't understand it:
QuoteCall Forward Numbers
There is one set of Call Forward Settings per voice service on the OBi, such that the settings apply to incoming calls on that service only. However calls may be forwarded to numbers on the same service or on another service. Therefore each call forward number stored in the OBi configuration MUST include call routing information to let the device know which voice service should be used to forward the call to. The general format of a call forward number is:
TK(number)
Note: TK is the abbreviated name of a voice service.
Valid values of TK are SP1 for the SP1 Voice Service (with ITSP A or B), SP2 for the SP2 Voice Service (with ITSP A or B), LI1 for the PSTN service (on the LINE Port), or PP1 for the OBiTALK Service.
The number to forward to must be in the final form that is acceptable by the service provider. OBi will not apply any Digit Map or Call Routing Rules on it.
Examples: SP1(14089991234), PP1(ob200333456)