You might look in your RADIUS accounting 'detail' log files and see what
port type the PM3 logs for 'modem' versus 'isdn' calls, then use the port
type as a radius check option.
The easiest method is to put a check item on the non-ISDN customers so
if they try to connect with ISDN they get an invalid login. If you want
to get fancy, you could also add a DEFAULT entry that matches on ISDN
calls that 'fall through', and send them to a menu telling them how to
subscribe for your ISDN service :-)
> if not, is there any way
> to monitor whether a user dials up with ISDN or analog (so that they may
> be billed accordingly).
You could use those same detail logs to view who has logged in on each
port, and what type of connection it was (ISDN vs modem?).
My log parser script doesn't store the port type, but it'd be child's play
to add it.