Would a simple default ACD/SCN work?
Log in with any 4 digits---Set will ring on DID...but each DID would require it's own CDN/DFDN as well. (Receive up to 10 digits from carrier on DID...At least, 1 more than an internal extension DN range.)
Log out ---Set will not receive calls on DID.
---NON DID SCR appearance - DN range for Internal calls. Make the DN the last 4 digits of the DID number.
Key 01 - SCN XXXX
Key 00 - ACD InCALLS
(DIG - Intercom key will ring as well but if you have an 81, I expect more than 99 sets -- a two digit intercom number won't work in the multiple groups needed.)
KE407122
"The phone was working fine before it knocked over my coffee.