Is it possible for a 7912G IP Phone to have a Primary Number and also a shared number with multiple phones. I want each phone to have its own extension, but multiple phones to ring for a specific number.
I'll try and fill in for Paolo for a moment (+5 "P")
Dual-line ephone-dns can also use overlays. The configuration parameters are the same as for single-line ephone-dns, except that the huntstop channel command must be used to keep calls from hunting to the ephone-dn's second channel.
The primary ephone-dn in a shared-line overlay set should be unique to the phone to guarantee that the phone has a line available for outgoing calls, and to ensure that the phone user can obtain dial-tone even when there are no idle lines available in the rest of the shared-line overlay set. Use a unique ephone-dn to provide for a unique calling party identity on outbound calls made by the phone so that the called user can see which specific phone is calling.
Shared-line Overlaid Ephone-dns: Example
The following is an example of a unique ephone-dn as the primary dn in a simple shared-line overlay configuration. The no huntstop command is configured for all the ephone-dns except ephone-dn 12, the last one in the overlay set. Because the ephone-dns are dual-line dns, the huntstop-channel command is also configured to ensure that the second channel remains free for outgoing calls and for conferencing.
ephone-dn 1 dual-line
ephone-dn 2 dual-line
ephone-dn 10 dual-line
ephone-dn 11 dual-line
ephone-dn 12 dual-line
!The following ephone configuration includes (unique) ephone-dn 1 as the primary line in a shared-line overlay
!The next ephone configuration includes (unique) ephone-dn 2 as the primary line in another shared-line overlay
From this good CME doc;