I finally managed to get my USB-Serial converter running on the Fritz!Box 7170.

So now I can use the Fritz!Box as a remote console to monitor my little server :-)

Hit Read more... to learn how to do this... 

To make this possible you need to modify the firmware.
I used Freetz 1.0 (http://trac.freetz.org/) and modified it in the following way: 

my converteer is baesd on mct-u232 so I had to include the usbserial and mct_u232 driver

Follow the default setup for Freetz.
(It's a good idea to choose the usbserial when running make menuconfig the first time)
If the new image works as expected on your Fritz!Box we can continue.

Do the following inside your Freetz dir and choose the appropriate driver for your converter (here we use mct_u232)

# make kernel-menuconfig

# make kernel-precompiled 

Now we have to patch the kernel/Config.in  so the driver will end in the new image.

patch -p0 <<-EOF
--- ../freetz-1.0-working/kernel/Config.in 2008-06-07 13:57:23.000000000 +02
+++ kernel/Config.in 2008-07-21 00:51:31.000000000 +0200
@@ -158,6 +158,10 @@ config FREETZ_MODULE_usbserial
  bool "usbserial.ko"
  default n

+config FREETZ_MODULE_mct_u232
+ bool "mct_u232.ko"
+ default y
+
 config FREETZ_MODULE_pl2303
  bool "pl2303.ko"
  select FREETZ_MODULE_usbserial
EOF

# make menuconfig

# wget http://alioth.debian.org/frs/download.php/2332/minicom-2.3.tar.gz
# tar -xvzf minicom-2.3.tar.gz
# cd minicom-2.3
# ./configure --host=mipsel CC=${PATHTOFREETZ}/toolchain/target/bin/mipsel-linux-uclibc-gcc --enable-cfg-dir=/etc --enable-dfl-port=/dev/ttyUSB0
# make
# cp -av src/minicom ${PATHTOFREETZ}/freetz-1.0/root/usr/bin/
# echo -e "pu port /dev/ttyUSB0\npu baudrate 115200\npu bits 8\npu parity N\npu stopbits 1\npu rtscts No" > ${PATHTOFREETZ}/root/etc/minirc.dfl

# modprobe usbserial
# modprobe mct_u232.ko

usbcore: registered new driver usbserial
drivers/usb/serial/usb-serial.c: USB Serial support registered for Generic
usbcore: registered new driver usbserial_generic
drivers/usb/serial/usb-serial.c: USB Serial Driver core v2.0
drivers/usb/serial/usb-serial.c: USB Serial support registered for MCT U232
usbcore: registered new driver mct_u232
drivers/usb/serial/mct_u232.c: Magic Control Technology USB-RS232 converter driver z2.0

usb 1-1: new full speed USB device using ahci and address 3
mct_u232 1-1:1.0: MCT U232 converter detected
usb 1-1: MCT U232 converter now attached to ttyUSB0

Now fire up minicom and enjoy the serial console

If you installed Freetz WEBCFG add "usbserial" and "mct_u232" to the modules autoload list so you will not have to load them manually every time you reboot your  Fritz!Box

If you want to know how to configure a serial console on a Linux PC, take a look here:
http://www.vanemery.com/Linux/Serial/serial-console.html

You can view the discussion here:
http://www.ip-phone-forum.de/showthread.php?t=171069