A tool box in one hand.
A 12x12x12 box (or 2) with a part in the other.
A clipboard tucked in the back of your pants.
Walk from a parking garage, down the lobby, up 10 floors and down the hall.

A laptop would just be left in the truck. Then they would pull their cell out and call the shop. "I just need that one adjustment" "Can't you just look it up for me?"

You have an extra man burning time and a laptop just waiting to grow legs and walk away.

A PDA cell will be with them all of the time. No excuses.