Surely the proximity sensor would lock the screen when it is in your pocket though? I've never had a touchscreen device like this but from what I've read the iPhone locks the screen when you put it up to your face to take a call - I'd be surprised if it didn't also lock it when you put it in your pocket and I'd be disappointed if the N900 didn't do this too. At least it has a proximity sensor so it shouldn't take much code to make it do this if it doesn't out of the box.