Question about UDN

I just wanna know what UDN is exactly , and is it available for all of us ? can i join for example ? because for me i have at least 1 or 2 questions everyday that i want to ask and Answerhub it self seems to be not enough for me can you please tell me first what is UDN and what are the places that i can ask my questions and get respond ? any forums or anything .

Thanks in advance

Access to technical support for custom licensees through UDN.

Check the Link, I hope that answers all your questions.
link text