What is the Sharīʿah ruling on a man talking to a woman on the phone, using vulgar and explicit language, to the extent of engaging in indecency over the phone? Is this practice considered Zinā (fornication/adultery)? Does the ruling differ if both parties are unmarried, or if one of them is married, or if both are married? Is there an expiation for this upon repentance?

It is not permissible for a man to speak with a woman who is a stranger to him except out of necessity and with permissible speech. As for lewd talk and engaging in vice over the phone, it is an abomination and a metaphorical form of zina (unlawful sexual intercourse). It is haram (forbidden), and its prohibition intensifies if it is with a married woman or if it originates from a married person. The expiation for this act is sincere repentance. The Muslim must feel the enmity of Satan and the soul that incites to evil, and must strive against his own self to be saved from evil and to draw closer to Allah.