Two 7941 phones that have a personal extension on button 1 and need to receive general PSTN calls on button 2. The line on button 2 will be shared on both phones. Both phones need to ring on an incoming call. When the a call is answered on button 2, the second call to button 2 needs to ring on both phones. When two calls are answered on button 2, the third incoming call needs to be forwarded to an autoattendant. Any call unanswered (first or second) needs to forward to the autoattendant as well.
The key is creating two ephone-dns with the same number, using huntstop channel on both but no huntstop on one, and preference 1 on the second. Then call-forward noan both to voicemail, but only call-forward busy on the second. Then set call-waiting ring on both. Now, when associating these ephone-dns with an ephone button, use c rather than o.
Below is a sample of two phones with three shared ephone-dns (two numbers) overlayed on button 2. All calls ring all the time unless the button is already handling 2 calls.
Hurray!
ephone-dn 100 dual-line
call-waiting ring
number 2100
label MBL 2100
description MBL 2100
name MBL 2100
call-forward noan 2223 timeout 24
huntstop channel
no huntstop
hold-alert 30 originator
!
ephone-dn 101 dual-line
call-waiting ring
number 2101
label AA Zero Out
description AA Zero Out
name AA Zero Out
call-forward noan 2222 timeout 24
hold-alert 30 originator
!
ephone-dn 102 dual-line
call-waiting ring
number 2100
label MBL 2100
description MBL 2100
name MBL 2100
preference 1
call-forward busy 2223
call-forward noan 2223 timeout 24
huntstop channel
hold-alert 30 originator
!
ephone 4
username "user2104"
mac-address 0000.0000.0000
type 7941
button 1:104 2c100,102,101
!
ephone 6
username "user2106"
mac-address 1111.1111.1111
type 7941
button 1:106 2c100,102,101