Problems with mgetty/pppd and more than one modem

Hello,

I have problems with configuring mgetty/pppd in order to support two
dial-in modems. The configuration of a single modem works fine.
Actually the only problem I have, is how to tell pppd what device name
to use in order to find the proper options.<ttyname> file. The only
way I found out so far is to add it to the parameter list of the
auto-ppp entry in /etc/mgetty+sandfax/login.config:

/AutoPPP/ - a_ppp /usr/sbin/pppd /dev/ttyS0

This works fine as long as I only use a single modem. But how can I
tell mgetty to automatically pass the device name as a parameter to
the /usr/sbin/pppd call?

The funny thing is that all configuration examples in the internet
include this line in the login.config:
/AutoPPP/ - a_ppp /usr/sbin/pppd

How can this work at all? The pppd man page says, that the
options.<ttyname> file is chosen according to the device name passed
as a parameter to pppd! At least it does not work on my machine. If I
use this configuration, pppd does not send the proper ip addresses to
the peer but uses 0.0.0.0 instead.

Thank you
Jürgen