If it is a "Transceiver" one set of terminals might well be 8 ohms... The Microphone, The piezo will measure as a capacitor and I won't even begin to try to guess the capacitance as I know nothing of the Er or dielectric constant or the piezo material (barium titanate, typically) or it's size. however a 4K7 resistor in series with a 5V supply (polarity unimportant) and note a small click with the pair that has no continuity with each other... Thee resistor will limit the current to 1 mA. not enough to produce much noise from the microphone (magnetic microphones make inefficient speakers) but since the piezo doesn't require much current to operate it should be a noticeably louder "click"...
Bob