Um, well, actually..
an isdn modem is not a modem.
A "modem" is defined as a "modulator/demodulator". If you're not sure what that means, Webster 1913 has an excellent writeup on "modulate". Read it now.
Essentially a modem varies the pitch of a sound-- or rather, the frequency of an analog signal-- back and forth for the purpose of conveying digital information through that analog signal.
ISDN "modem"s do not do this, in any sense of the word. They do not use an analog signal. ISDN is a pure digital channel. Thus, an ISDN "modem" just transfers information across the digital ISDN channel. It does not modulate. It does not demodulate. It is not a modem. If someone takes an ISDN modem and writes "router" on it, they would be wrong, i guess, but that's ok because if they took an ISDN modem and wrote "modem" on it they would be wrong as well.
In the meanwhile, mdn is NOT WRONG, because there is, in fact, an international conspiracy to mislabel ISDN products as "modem"s. This conspiracy is called "The ISDN industry". Their evil goal is to speak to clueless people in the clueless people's own language, thus causing the clueless people to understand what the conspiracy's products are and possibly even buy them. Meanwhile what little meaning was left in technical jargon is perverted and dumbed down the tubes. Deciding whether or exactly how much evil this is, i will leave as an exercise to the reader.
You're no match for my pedantic level!
This has been a non-nitpicked node rescue