I was on an IFR arrival into Houston a while ago with busy Approach Control, when I heard the following exchange:
Approach Control: “N1234 say altitude.”
N1234: “Altitude.”
Approach without hesitation and very patiently: “N1234 say the altitude you are flying.”
N1234: “Oh, 5,500 feet.”
Approach: “Thank you. Altimeter 29.93.”
Mark Robertson Alvin, TX