The Billboard, January 1, 1921, page 10:
SINGS OVER RADIOPHONE
New York, Dec. 24.--Vaughn De Leath, who recently toured the Keith Circuit with Marie Cahill, this week gave her second concert of popular songs over the De Forest Radiophone from the World Tower Building. Miss De Leath is said to be the first singer of popular songs to demonstrate her voice over this new transmitting device, and after her first concert, a week ago, received scores of letters from sailors and wireless operators thanking her for the entertainment. She was assisted by Mario Perry, accordionist, who is now being featured at the Cafe de Paris.