Question about GPL Software in Telekom Speedport W900V

[Ralf Friedl]

T-COM (Deutsche Telekom, German Telekom) sells the device 'Speedport 
W900V', a DSL Router with phone/ISDN/DECT functions.

1.
This device uses a Linux-based firmware (Linux 2.6.13.1).
T-COM offers partial sources at this address: 
http://www.t-com.de/dlp/eki/downloads/Speedport/Speedport%20W%20701%20V/GPL-r4264-8mb_26-tar.bz2 

One problem is that this won't build as is because it contains symbolic 
links to files in '/home/jpluschke/...', probably the home directory of 
one of the developers, which are not included in the download.
Even if the symlinks are resolved, there are some kernel modules without 
source that are present in the binary firmware which are loaded into the 
kernel.
These modules are: kdsldmod usbahcicore isdn_fbox ubik2 tiatm Piglet.
Is this legal under the GPL?

2.
Especially the module isdn_fbox seems to use the file skbuff.h and the 
inline-functions defined there. The module contains references to skb 
funktions:
       U alloc_skb
       U __kfree_skb
       U skb_over_panic
skb_over_panic is called from inline-functions from skbuff.h in case of 
errors.
That means that they don't just include the header files, the code from 
the inline funktions is part of the generated binary object file, and 
the kernel include files are not LGPL.
Is this legal under the GPL?

3.
GPL section 3 states: "complete source code means ... plus the scripts 
used to control compilation and installation of the executable".
This device has the firmware on an upgradable flash memory. But the 
firmware on the device as sold will only accept for update a firmware 
digitally signed by T-COM.
As this key is needed to compile and install a modified firmware, is the 
key considered part of the source and are they violating the GPL by not 
distributung the key?