Apple Macintosh 6500 - Manual (Page 91)

Setting up an ISDN line
If you’re interested in setting up an ISDN line, first contact your local phone
company to see if ISDN service is available at your location. Your phone
company can also provide specific information about monthly charges and
usage fees. (Your phone company may also charge an installation fee, which
may be waived or refunded if you agree to keep the ISDN line for a specified
amount of time.)
In addition, you also need to purchase and configure an ISDN terminal
adapter, which connects to the external modem port on your Macintosh and
to the ISDN line. (ISDN terminal adapters are often called “ISDN modems”
because they are somewhat similar to modems.)
Some ISDN terminal adapter models may be difficult to configure with the
network configuration of your employer or internet service provider. Work
closely with your computer network administrator or internet service provider
to make sure you purchase a compatible ISDN terminal adapter.
91 Connecting Your Computer to a Telephone Line