GNU/Linux software on Siemens and Da-San ethernet switches

Hello,

I am working in a data carrier company in Nairobi, Kenya, and we are 
currently deploying a metro-ethernet through our contracted partners of 
Siemens, Germany. Siemens have recently acquired the Korean company 
Da-San, and they have re-branded Da-San's line of ethernet switches as 
Siemens Surpass hiD6610 and hiD6625.

After having worked with these switches for a while, I noticed that they 
are running an ordinary Linux kernel and some GPLed software (such as 
"busybox", plus of course the GNU coreutils), while the user interface 
and the advanced bridging and routing protocols are implemented via 
IPInfusion's commercial ZebOS software suite.

Now, for various reasons I would like to be able to tweak (you could 
also say "fix") the switch software, so I've approached various high- 
and low-level Siemens and Da-San people to provide me with the source 
code, but to no avail whatsoever. The (very badly written) user manual 
for the most recent switch Surpass hiD6610-S311 says on its first inside 
page that the "source code of the GPLed parts of the software" (my 
paraphrase) will be made available on request. It was a bit hazy about 
how that request is to be made (the web address actually terminates in 
an ellipsis, and the whole manual is still in an alpha state), but there 
was a Korean fax number, to which I have duly faxed my request, again to 
no avail.

I have since learned from the list FAQ that the hardware makers are also 
meant to release build scripts and such like, and also everything 
pertaining to the most current version. Since the firmware keeps getting 
hotfixed, I would be really happy about access to the current develpment 
tree. But so far all my requests are completely ignored.

I would appreciate very much any information on how I can convince 
Siemens/Da-San to release that source code.

Many thanks!

Thomas Köppe