Siemens SL2-141-i ADSL2+ Router with Wi-Fi 802.11g 54Mbps. It is most similar to the RTA1025W from Dynalink After changing the Board ID you can use these firmwares.

At time of writing, it is not straight-forward to run OpenWRT on this device due to strict checks of the image format and board ID (RTA1025BW_16)

See also https://dev.openwrt.org/ticket/6920

But you can change the Board-ID using cfe-environment and serial console, then you can use the RTA1025W-Builds, e.g. for OpenWRT Backfire.

system type             : RTA1025BW_16
processor               : 0
cpu model               : BCM6348 V0.7
BogoMIPS                : 239.20
wait instruction        : no
microsecond timers      : yes
tlb_entries             : 32
extra interrupt vector  : yes
hardware watchpoint     : no
VCED exceptions         : not available
VCEI exceptions         : not available

The pinout of the serial console port on the Sl2 is as follows

Serial connector (white, look at the pictures)
 ___
| 1 | -> Rx
| 2 | -> Tx
| 3 | -> GND
|_4_| -> +3,3V


 ___
|USB| For orientation...
|___|

Connect to the board using a serial console cable, boot the device and stop it booting by pressing space to get on the cfe-prompt:

CFE version 1.0.37-6.8.5 for BCM96348 (32bit,SP,BE)
Build Date: Tue Jan  2 19:42:28 CST 2007 (michaelc)

Boot Address 0xbfc00000

Flash Config: CS0(1fc00009,1f),Base(bfc00000),Size(4MB)
Ethernet Switch Mode 00000000
found@block 8

Board IP address                  : 192.168.1.1  
Host IP address                   : 192.168.1.2  
Gateway IP address                :   
Run from flash/host (f/h)         : f  
Default host run file name        :   
Default host flash file name      : bcmModelName_fs_kernel  
Boot delay (0-9 seconds)          : 1  
Board Id Name                     : RTA1025BW_16  
Psi size in KB                    : 24
Number of MAC Addresses (1-32)    : 4  
Ethernet MAC Address              : 00:16:e3:xx:xx:xx  
Serial Number                     :   
Memory size in MB                 : 16
CMT Thread Number                 : 0

==== Press space key to stop auto run (1 seconds) ====
Auto run second count down(before hit space key):

At cfe-prompt type 'b' followed by enter:

CFE> b
Press:  <enter> to use current value

Board Id Name (A-Q)
RTA1046VW        -------- A
RTA1046BVW       -------- B
RTA1052VW        -------- C
RTA1052BVW       -------- D
RTA1052V         -------- E
RTA1052BV        -------- F
V2091_BB         -------- G
V2091            -------- H
V2090            -------- I
V2110            -------- J
V2500V_BB        -------- K
RTA1025W_16      -------- L
RTA1025BW_16     -------- M
RTA1505W_16      -------- N
RTA1505BW_16     -------- O
RTA1046VW_32M    -------- P
RTA1046BVW_32M   -------- Q       :[M]:  L
Number of MAC Addresses (1-32)    :[4]:  
Ethernet MAC Address              :[00:16:e3:xx:xx:xx]:  
Serial Number                     :[]:

Save and Exit  (y/n):y

Save your new configuration to nvram........done

Press any key to reset the board: 

You have to choose 'L' instead of the predefined 'M' to switch to Board-ID RTA1025W_16!

After saving and reboot you can flash any RTA1025W_16-based openwrt-Firmware.

The source code is hosted at alibstechnologies because they bought the Siemens broadband company.

Here's the source code.