AT&T SYSTEM 25 User Manual page 9

Ringing Tones
System 25 signals you with three distinctive rings. The rings
and their descriptions are listed below.
INSIDE CALL
Your call is from a person inside your company.
OUTSIDE CALL
Your call is either from the Attendant or someone outside your
company.
PRIORITY RING
ring)
Your call is either a callback because the station or outside line
you requested is now available, or your call is being set up
remotely via Third-Party Call Setup (a data feature).
DDCs and PDCs
When your System 25 was installed,
were assigned to data terminals and
were assigned to voice terminals.
If you don't have exclusive use of a voice terminal, you may
have been assigned a Floating Personal Dial Code (FPDC).
For Additional Information
See your System Administrator if you have any questions or
would like additional information about your System 25 features.
4
(one long ring)
(two short rings)
(two short rings and one long
Data Dial Codes (DDCs)
Personal Dial Codes (PDCs)