Hi, this is a long shot, but here goes! You could renumber a calling group to 12. Then either make the member of calling group 12 be the phone or phones you want it to be. The issue is the voice mail coverage on no answer.
In theory, if you make a calling group 12 and set it as auto log in type, you will need to make an ES2 (available) button (programming code *44 on a button with a light) for the phone that is the member of calling group 12 or else the phone will not receive calls. Calling group 12 will also have to overflow to 770 (assumed voicemail number). The issue is that if the extension that is the member of calling group 12 is on the phone, the next call will overflow to voicemail box 12 as no other members are available. Also, if you turn off the "available" button, there will be no available phones so all calls will go to mailbox 12. Not terrible, but the issue is when you are not at the desk, forget to turn off available, and a call comes in. It will ring indefinetly.
You could opt to make the group type auto-log out instead, which would cause the available button to go out if you don't get to the phones in a few rings and send calls to voicemail 12. The issue is that you may return to your desk and not see that you were logged out automatically and therefore miss more calls.
The message light can be dealt with under group calling>message>xx> where xx is the actual extension of the phone that is the member of calling group 12. It is in effect, a group mailbox light owner.
I have to sleep on this one! I also have a loop around idea if you have a free tip/ring port on an 012 or 016 basic mod and a free outside line port. More to follow.
mike