Since there is a pretty good chance, that my change of phone companies will occur while I am away, I’ve setup a remote dialin via my mobile phone.

Small HowTo (based on: Peter Bieringer’s isdn dialin howto):

Serverside

server: Debian Sarge Linux
hardware: AVM ISDN Fritz PCI card
software: mgetty package, working isdn environment (2.6.9 with fritz_pci module)

/etc/mgetty/mgetty.config
# Login over ISDN & V.110 (GSM)
port ttyI1
init-chat “” ddd+++dddATZ OK AT&E&R9600S19=0 OK
modem-type data

/etc/mgetty/login.config
replace this line:
/AutoPPP/ - a_ppp /usr/sbin/pppd auth -chap +pap login debug
with:
/AutoPPP/ - a_ppp /usr/sbin/pppd file /etc/ppp/handydialin

/etc/inittab:
T0:23:respawn:/sbin/mgetty -x 9 -s 9600 ttyI9

(don’t forget to restart with init q!)

/etc/ppp/handydialin:
auth
+chap
-pap
debug
name dialin
#kdebug 5
ms-dns 192.168.1.1
ms-wins 192.168.1.1
192.168.1.1:

/etc/ppp/chap-secrets:
joe dialin “password” 192.168.1.5

Clientside

client: Windows XP Pro
hardware: Sony Ericsson
software: default installation will do

Go to the device manager, and click on the properties of your modem.
Go to the Advanced tab and enter AT+CBST=71,0,1 in the initialization command field.

Create a new connection, enter the configured msn as destination and enter the username and password that you’ve used in chap-secrets (joe/password). Go to the network tab, click on the PPP properties button and select only the first item. (You can activate software compression later on, if everything else works.)

Start the connection, the mobile phone should dial and negotiate everything. That’s it.
In case something did not work, syslog should provide enough clues.