While trying to configure the isdn subsystem with the tools provided, I came across isdnconf. There seems to be no manual page available for that program, and the -? and -h options don't provide much help. There is little help available on ISDN as it goes. The only package that seems to contain a man page for isdnconf is in Caldera OpenLinux 2.3, however, the link to the isdn4k-utils is broken on the Caldera site...
The manual page is added in the fix for bug 7585. 7585 is resolved in Rawhide and available from ftp://ftp.redhat.de/pub/rh-addons/isdn/testing. Thanks!