The voice of a woman is not awrah but Allah ordered them not to soften their voices. I wouldn’t suggest women to be public speakers to non Mahram or give a sermon that men can listen to as this is not what was at the time of the Prophet salla Allahu alaihi wa sallam and his companions.

Women should only address women.

Sir is a womens voice haram for other non mahram to hear ? i mean can she give religious sermons on radio ? in pakistan there is a women scholar dr farhat hashmi she runs an organization called al-huda .