The device comes preinstalled with an unknown Linux-distribution. You may log in with telnet @ 192.168.1.1 (default config) to get a busybox-shell. It seems that the device is a clone of Aztech HW5503g (power supply is labeled “Aztech” and the hardware specs and WebUI are the same except for the branding) but you won't mess up your installation flashing the device using the WebUI (in my case, so be careful, I won't take any responsibility for bricked devices!).

→ Install OpenWrt (generic explanation)

Due to the fact that the device comes with Linux preinstalled, you can use the precompiled Attitude-Adjustment Image following this link: http://downloads.openwrt.org/attitude_adjustment/12.09/ramips/rt305x/openwrt-ramips-rt305x-all0239-3g-squashfs-sysupgrade.bin

1.) Reset your device to factory defaults.

2.) Navigate to the firmware section.

3.) Use the image provided above to flash.

4.) Wait for OpenWrt installation.

5.) You're done .

The image comes with luci preinstalled so you are able to login to the web ui @ 192.168.1.1. There is a bug in this version regarding the password-settings. It is not possible to change the root-password using the Web ui! You need to login via shell to change it via “passwd”.