Many telephone system users have the need to add doorphones to their phone system.  It is an added level of security for areas that the door needs to be monitored for entry, and it simplifies allowing access by ringing all phones and giving the user the ability to buzz the door open from their desk.  The Avaya IP Office Phone System operates much differently than most business phone systems when it comes to door phones and contact closures.

Follow up:

The Avaya IP Office Essential Edition, as well as the Avaya IP Office Partner Edition, the phone system only supports up to 2 door phones and contact closures.  With the IPO Partner Version, the doorphones will not operate properly using an Analog Station Port such as on the ATM Combo Card, Phone2 Card, or Phone8 card.  You must connect the doorphones to an ETR Card.  In the case of the former Norstar Door phones, these will not work at all on the Avaya IPO Essential or Avaya IPO Partner.  Another issue that comes up on both systems is that the Door Release Contact, or Contact Closure, only works with DC mechanisms.

An alternative option that works with both versions of Avaya IP Office, is the Viking Door Phone Control Unit C-2000B.  This unit can handle up to 4 Viking Door Phones, and also includes Caller ID to indicate which door phone is calling, and an AC/DC door release contact for each door phone.  It also only requires a single pair cable to connect to the controller.   You can use a variety of Viking Door Phones on this control unit to accommodate your needs, such as units with weather protection, or units with video cameras built in, etc.  The Viking C-2000B is compatible with units such as the E-10A or E-35-EWP, E-40, or E-50, etc.