Regarding UC520, I beleive the default configuration comes with quite a few access lists configured. So if you have to explicitly add a statement allowing that. I am adding quite a bit of information on questions like these on my <a href=”http://www.questivity.com/uc520.html”> uc520 VoIP solutions page. </a>
If you still cannot get this resolved, send me an email and I’ll try to get the answer posted here and also on my website on the FAQ.