It is not always with me. We are not inseparable.
But they can handle that like they handle photo radar tickets (which only prove your CAR was speeding). They assume that since it was your phone, it was with you. Then they give you a chance to rat out whomever had your phone if it wasn't you, and there's not much you can do about it, especially since it's only a "civil" matter and not criminal. The real flaw I see in the idea is proving who was driving. If there are four people in a car and they each have a couple smartphone/tablets, etc., only the driver is liable. How are they going to figure out who to send the ticket to, and what prevents multiple tickets from being issued to multiple devices even if they all belong to the guilty party?