Yup, same problem here. Of course, the first time it happened it was because I cut a custom screen protector and didn't leave a hole for the speaker.

But since adding the speaker hole, I still have a sound drop-out problem. Usually I just switch to speaker-phone. I'll see if pressure makes a difference.

Anyone notice a correlation between screen backlight and sound drop-out? That might indicate a prox sensor issue.

Looking at it closely, I'm guessing the prox sensor is just an infrared led/sensor. I'll try putting my finger over the prox next time it happens.

My N95 was unbelievably rugged. I'm hoping the N900 has the same build quality.