Phreck: You aren't alone. My wife and I both have the same exact problem. Different amounts of pressure yields different results and it's as if there is a loose wire somewhere in the phone. I still don't know what to do but I've gotten used to it to the point where from now on I'm always making sure I press super hard while taking calls. My wife on the other hand has given up and just uses speaker phone from now on.

I don't know if this noise cancellation has anything to do with it. Here is a link where someone else talks a little more in depth about it:

http://talk.maemo.org/showthread.php?t=37590&page=2

Let me know if you find a solution to this. I have yet to reflash my phone but I doubt that will fix the problem as others have said it didn't help them and some have said the problem went away after doing a fresh reflash with the new firmware update.