Cisco 700 - Manual (Page 50)

Connecting an ISDN (Digital) Telephone
Cisco 700 Series Router Installation Guide 4-2
Caution Do not connect the router telephone ports to the telephone wall jack.
These ports are not meant for direct connection to a public network. This
connection can damage your router.
Connecting a Self-Powered Digital Telephone
You can connect an ISDN telephone to the Cisco 761, Cisco 765, Cisco 771, or Cisco 775
only through an external NT1 connector. If you are connecting an ISDN telephone directly
to the Cisco 762, Cisco 766, Cisco 772, or
Cisco 776, connect the ISDN telephone cable
(provided with the ISDN telephone) to the RJ-45 port labeled ISDN S/T on the rear panel
of the router. Cable the ISDN wall jack to the port labeled ISDN U. (See Figure 4-1.)
Refer to the instructions provided by the manufacturer of the telephone.