If you use the adapter included with delivery you can use both of the FRITZ!Box's "FON S0" sockets, without the adapter you can only use one socket. You can use an ISDN distributor or S0 bus cabling to connect up to eight devices to each socket at the same time, for example telephones or a telephone system. The FRITZ!Box can provide power to one ISDN device, but the other ISDN devices must use their own power supply.

You can use the following ISDN service indicators with devices connected to the "FON S0" socket:

• Voice (service indicator 1)
• Data (service indicator 2)
• Audio 3.1 (service indicator 4)
• Telephony (service indicator 16)
• Fax G2/G3 (service indicator 17)