I've now found a method to screen anonymous calls with my Obi110 which I think will satisfy my requirements.
Hopefully the following method will stop nuisance ( automated ) calls yet give an option for real people to still get through.
1) I recorded the following message in Auto Attendants "User1 Prompt"
"Welcome to Obi call screening.
The number you are calling is not accepting anonymous calls.
Please speak your name, then dial 1 to be connected."
2) User2 Prompt was left blank.
3) I then configured Auto Attendant as show in the following screen capture.

Note:
I don't use the Obitalk service.
4) Configured the Line Port.
InboundCallRoute: {(?):AA},{(00xx.|01600469009):},{ph}
Anonymous calls don't ring the phone, they are sent to the Auto Attendant which plays the message in user1 prompt.
When the caller dials 1 the call is put through and the phone rings, if the caller dials any other number the "goodbye" message is played and the call is disconnected.
I've included "please speak your name" prompt purely for affect, the response is obviously not recorded.
Any comments / suggestions gratefully received.