Biggest german isp ships router with free firmware??!

Hi everybody!

One of the biggest german isp's is called 'Deutsche Telekom' and i'm a costumer of them. Normally, they sent you a router of the 'speedport series' when you get your internet access, and so did i.
I wanted to check out if i can install the libre router software...dd wrt(? Sorry, i don't recall the name in detail...) when i found that the source code for the firmware was already available and licensed under the gpl.
I tried to copy the link, but orweb doesn't want to... So search for 'telekom speedport open source'.
Sorry for the term but otherwise you won't find it.
Of course i'm suspicious, like, maybe they kept a crucial part proprietary as a back door...and i also don't know if you can actually install your modified versions without problems.
But still, i'm quite excited about that.
What do you think? Do isp's in your country the same or is it rather an exception?