I drive a 4WD van, so my eye level is high enough to look down into most other cars. I often see drivers with mobile phones in their lap. The phone screen usually being lit up because they're texting or making a call. If you follow one of those idiots, they're usually wandering all over their lane.
In case some of our USA friends are wondering about this (most USA states don't ban the use of phones while driving). It's against the law to hold a mobile phone while driving in Australia. The definition of "holding" a phone includes having it resting on your lap. You're not even allowed to pick it up and hand it to a passenger. A driver is only permitted to speak on a phone that is fixed in a cradle and can be operated hands-free.
I actually think that drivers shouldn't engage in any kind of phone use, including hands-free devices, because it diverts the focus of your attention to issues outside the driving environment. I once got a speeding ticket because I was talking to my boss on a hands-free phone and wasn't paying attention to the speed limit. He was a little surprised when I told him I'd have to hang up because there was a cop pulling me over. After that incident, I told my work colleagues that I wouldn't be answering any phone calls while driving. I'd call them back when I had somewhere to pull off the road and stop.
I now have a setting on my phone (iPhone) so that it automatically goes into "do not disturb" mode when I'm driving. Incoming calls go straight to voicemail without the phone ringing and it doesn't give text alerts. I presume it's activated by the phone's internal GPS. It must work out whether it's moving along a road at a speed greater than walking pace. It sends the caller a text message that says I'm driving and will get back to them later.