ISDN terminal equipment (ISDN phones, ISDN PBXs) can be connected to the ISDN S₀ port of your FRITZ!Box.

The following steps are required to start operation of the ISDN terminal devices at FRITZ!Box:

• Connect the ISDN terminal equipment to FRITZ!Box.
• Enter your Internet numbers and your fixed-line network numbers in FRITZ!Box.
• Assign numbers to the ISDN terminal devices.

Main phone number

ISDN terminal devices to which no number has been assigned conduct outgoing calls with the number entered in the "Main phone number" field.

Existing numbers

The "Existing numbers" list displays the numbers you have already entered in the FRITZ!Box. These numbers can be specified at the ISDN terminal equipment as Multiple Subscriber Numbers (MSNs) and define the kind of connection established for outgoing calls.

Note:
If numbers are registered on the ISDN terminal devices, but are not included in this list, enter these numbers in the FRITZ!Box as well.

Additional Features for ISDN Terminal Devices

To configure additional convenience and performance features, note the following:

Call rejection on busy (busy on busy)

Enable this option if callers who call during a telephone conversation should hear a busy signal. Callers receive a busy signal when

• the setting "Call rejection on busy (busy on busy)" is active and
• you are currently conducting a call on an ISDN telephone, and
• the number over which you are conducting the call has been configured on the ISDN telephone.

Callers also hear a busy signal when the telephone number has been configured on more than one ISDN telephone. The call will not be signaled on any ISDN telephone.

Connected line identification restriction (COLR)

By default, the MSN (Multiple Subscriber Number) of the telephone called is transmitted to the caller. If the caller has enabled the ISDN feature "COLP" and you take the call at another telephone, the MSN of this telephone will be displayed. In this case the MSN of the telephone actually conducting the call remains concealed from the caller when the "Connected line identification restriction (COLR)" feature is enabled. The caller's display will continue to show the MSN she or he called.

Message waiting indication on the telephone (MWI)

Many telephone carriers supply their customers with mailboxes on which messages can be stored in various formats.
When you enable the "MWI" function, new messages in your mailbox will be displayed in the Call List of your telephone. The options "only for the first new message" and "for every new message" define which of the voice mail, fax and e-mail messages will be displayed.