Wingsley said:
In "Mudd's Women", Magda hands Harry Mudd a communicator and tells him a subspace frequency to use in contacting Rigel XII. Mudd then hails the Rigel mining colony from deep space.
In TNG's "Silicon Avatar", Riker uses his commbadge to contact the Enterprise while the ship is still at warp in deep space.
Can we establish from these incidents that communicators in TOS and TNG are subspace transceivers, and that they have more than orbital range?
I'm pretty sure that communicators would be hybrid devices, operating in both the conventional E/M bands and in subspace mode, depending on the operator-selected settings. We know that "old style radio" is seldom seen in TOS-era times. But we also know that TOS-era communicators are CAPABLE of RF-frequency operation.
So, a communicator has as a minimum the following components:
1) A HIGH OUTPUT power cell (necessary to push signals powerful enough to reach high-orbit spacecraft... and the "sensitivity of the receiver" argument doesn't counter that, since the signal strength still needs to be sufficient to overcome background E/M noise).
2) A radio-frequency transmitter.
3) A radio-frequency receiver.
4) A subspace transmitter.
5) A subspace receiver.
(it's POSSIBLE that some of the above could be accomplished using a single mode/switchable device, but it seems unlikely)
6) Some form of display. (I think that the little round thing on the communicator is a visual display, not a "speaker microphone")
7) Some form of manual controls (five pushbuttons, at least two of which are also rotational controls).

Some form of audio (and I really expect video as well!) pickup.
9) Some form of audio output (and, I think, the ability to use the center display as a video output).
Now, a video input could be a pinhole device, the speaker could be in the case, and we see a little grill that would be the audio pickup. The electronics control elements would be very tiny indeed. So the majority of the package would be a power cell and the transceiver elements.
It's not unreasonable to assume that the grid is the r/f receiver antenna, and could also be the r/f transmitter element. The subspace antenna element would have to be internal, though.