The greeters at National do not have radios or any way to communicate from one side to the other.
The greeters may not, but the office in the garage certainly does. I had a resevation for a convertible, and asked if any Mustangs were available; There weren't any on the B side, but the employees in the office were able to call the A side, confirm that there were, and have one brought over. This is the kind of service that has won National my loyalty, even when they're not the cheapest.