What do you use for good clean, clear sound on 2 camera shoots for communication between camera operators (wireless)? I have a set of Nady Easy Talk PRC-3X, but get lots of interference and noise.
Maybe try www.locationsound.com too and sneak into their pdf catalog under ClearCom, Comtek, or any communication system... or simply write to them.
And have you tried these Motorola (toys look-alike BUT very performant) walkie-talkies with a good mic'ed headset ? That could be an unexpensive solution...
I have one hand on the zoom control - talk with the other hand.
If using auto-focus, it doesn't matter. If using manual focus, I try to focus ahead of time. If using manual focus on something moving toward or away from me, I don't talk during that time. As an alternative, the zoom controller also has focus buttons.
But, yes, there may be some times when you cannot respond immediately.