(I'm skill-deprived: I can hack kernels but I can't use a mailer.)

I recently got a pointer from Van Jacobson to a version of Linux
that includes an (ancient) NetBSD networking stack _plus_ a STREAMS
stack.   The STREAMS stack has ISDN support.  If anyone really
wants to spend time on this,  I can dig out the reference and
forward it.

I don't think the original author of this NetBSD(0.9?)+ STREAMS
has worked on this particular stack since early 1994.