348 - שמיעת המגילה ע"י טלפון וכיו"ב - Electronic Megillah: A Question of Essence

From Rulings and insights from the Lubavitcher Rebbe - Rabbi Chaim Wolosow by R Chaim Wolosow.

The Rebbe rules that devices like telephones transmit an electronic reproduction, not a direct human voice. As Halacha requires hearing a voice through the air, electronic means are invalid for the Megillah. Even in urgent cases, the human essence of speech is required to fulfill the mitzvah. https://www.torahrecordings.com/shulchan_menachem/orach_chayim/348