This is a problem that I had been facing with:
1. Leather case with Magnet. (Accepted that this is a known issue)
2. Leather case with a clip type lock. (The case causes the phone to answer, reject or silence the call.)
3. No casing of anykind. (Problem occurs when wearing jeans or trousers having tight pockets.)
4. Hard Silicon Casing. (Problem occurs when wearing jeans or trousers having tight pockets.)

Basically, I feel that the phone takes stray motion on the screen to be a valid touch. The reason is because of the phone's resistive touchscreen which seems to make every stray mark count as a valid press.

(ResistiveTouchscreen: A resistive touchscreen panel is composed of several layers, the most important of which are two thin, metallic, electrically conductive layers separated by a narrow gap. When an object, such as a finger, presses down on a point on the panel's outer surface the two metallic layers become connected at that point: the panel then behaves as a pair of voltage dividers with connected outputs. This causes a change in the electrical current, which is registered as a touch event and sent to the controller for processing.)

To do something about this, we have to change the way phones are answered or declined. One possible solution discussed in some other thread was using sliding techniques like in Apple's IPhone. Well, that said, I really have no idea how much longer this will take to get fixed but Nokia is Nokia.... a slowcoach when it comes to upates. But im sure it will come, if not officiall, some solution will come up in this forum in sometime, it always has...