Not true at all, but from a very early age we're taught to especaiily pay close attention to conversations we're having on the phone... We have to... We're missing a LOT of what makes human discourse possible.... facial expressions, body language... that kind of stuff (The same kind of stuff that's missing here)

So when we're on the phone, we attempt to block everything eles out so we can pay attention... It's not the same as having a conversation with someone who's in the car with you... Or the radio (Which is VERY easily push to the back of out attention 'stove' when we need to)

With a cell phone, it's the DRIVING that gets pushed back.