Okay … the first step was done by getting the box a ip and starting telnetd. But this cant be all. :)
So i was searching a bit around .. with the standard codec used for voip, the upload was round about 85-90 KBit/s, so its tamped. If there is started a other upload, its getting shaped and if the shaping isnt working well, my telephon session gets fucked.
The solution maybe using G.726-32 as primary Codec which need around 45 KBit/s:
So you need changing /var/flash/voip.cfg with
# nvi /var/flash/voip.cfg
audiocodecs = "G726-32", "PCMA", "PCMU", "G726-40", "G726-24";
You also need to add this lines to /var/flash/debug.cfg
killall voipd sleep 3 voipd -i 0
I also added this line into /var/flash/debug.cfg to start remote syslogging:
# /sbin/syslogd -R *IPSyslogserver*
Sucking too is the fact, that time/date isnt correct after reboot. This will be fixed on first successfull ISDN call, but this will never happen, when you arent using ISDN.

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Since most of this stuff is fixed in recent firmware images, my debug.cfg have these entries:
echo root:g04jh2E6nd1vQ:0:0:root:/var/tmp:/bin/sh > /var/tmp/newpasswdmv /var/tmp/newpasswd /var/tmp/passwd
/usr/sbin/telnetd
sleep 10
/sbin/syslogd -R <ip syslog server>