Call Back Under Berkeley 4.2

[Clayton Cramer]

I'm looking for a way for a remote user of our VAX to:

1. Dial in through our modem.
2. Give a phone number where the remote user is located (and perhaps
   validate the number).
3. Have the VAX call back on that phone number (to which is attached
   an auto-answer Hayes-compatible modem).
4. Allow the user to login in a fairly conventional manner.

There doesn't seem to be anything built in to Berkeley 4.2 UNIX to
do this, and I'm sure that lots of security-conscious installations
have already done this.  Please post the solution -- I'm sure lots of
other people have a similar need for this.