If we want to be sensible, I suppose a communicator would just act as a localised quantum scanner to send data back to the ship but that would mean you couldn't beam anyone up without one. Blakes 7 used this type of device . It's very logical and you can then understand the role of the transporter room as opposed to someone on the bridge flipping a switch and beaming everyone in a twenty foot radius to a random location . It is possible that the primary function of the transporter room is decontamination I suppose but they rarely seem to care about that since they cut out the sensual gel massage.
I would say it's the confinement beam that keeps the person in transit so you can beam up as many people as you have beam emitters, regardless of where you rematerialise them. It is tough to see how any device could maintain its own confinement beam while in transport though. :-/
Yes, but that isn't what I'm talking about.

It's like asking a shark to open wide, swallow itself, and vanish. It's like asking a vacuum cleaner to suck itself up and vanish. And that's not even to mention the problem of a de-materialized device still able to perform the function of re-materializing things.
OTOH, I'm totally onboard with site to site transport, where the Transporter room locks onto you down on the planet and beams you directly to sickbay, let's say. The machine can do that just by using its beam up and beam down functions and skipping the middle-man pad.