The default fon2100 was useless to me so I decided to put http://openwrt.org on it.

Screenshot of the webinterface before flashing the device:

Hacking the device to gain ssh access to prepare the firmware flash process
Flashing the device
Upgrading OpenWrt

backup configuration files first:

/etc/config/*
/etc/dnsmasq.conf
/etc/firewall.user 

cat /proc/mtd 
dev:    size   erasesize  name
mtd0: 00030000 00010000 "RedBoot"
mtd1: 000c0000 00010000 "vmlinux.bin.l7"
mtd2: 006f0000 00010000 "rootfs"
mtd3: 005f0000 00010000 "rootfs_data"
mtd4: 0000f000 00010000 "FIS directory"
mtd5: 00001000 00010000 "RedBoot config"

First the kernel is updated 

cd /tmp
wget http://downloads.openwrt.org/kamikaze/7.09/atheros-2.6/openwrt-atheros-2.6-vmlinux.lzma
mtd -e vmlinux.bin.l7 write openwrt-atheros-2.6-vmlinux.lzma vmlinux.bin.l7

and second the squashfs image 

wget http://downloads.openwrt.org/kamikaze/7.09/atheros-2.6/openwrt-atheros-2.6-root.jffs2-64k
mtd -e rootfs -r write openwrt-atheros-2.6-root.jffs2-64k rootfs

After the reboot the router has following settings: 

LAN: 192.168.1.1/24
WAN: DHCP
WIFI: Disabled
Telnet: Enabled until root password set
SSH: Used after setting root password