I have this problem too with the top right softkey. I've noticed it only happens when the phone is warm, in my pocket or in direct sunlight for example. I think its poor build quality thats the problem here.
So you would recommend opening the phone up? That's what I was thinking, but wasn't sure if it would do any good. Maybe I'll pop out the keypad and see what's going on in there.
Hmm forgot what screwdrivers I need.. thanks Search button! (siGH)