Reference: al-Muntaqaa min Fataawa Shaykh Saalih al-Fowzaan – Volume 3, Page 300, Fatwa No.441
Question: Is there any legal (Sharee’ah) prohibition in replying to the greeting (as-salaam) of the woman on the telephone or in any other [circumstance], or [her] replying to the greeting (as-salaam) of the man on the telephone?
Response: There is no harm in a man replying to the greeting (as-salaam) of the woman on the telephone or in any other [circumstance], and [likewise] a woman replying to the greeting (as-salaam) of the man so long as they protect themselves against [any] fitnah; And this is based upon the general command of the Prophet ﷺ in replying to the greeting (as-salaam).
Likewise, there is no harm in a telephone conversation between a man and a woman [so long as they remain] within the constraints of necessity.
As for a dubious conversation or a conversation in which there is fear of fitnah, then that is not permissible because it is a means to that which is prohibited (haraam). Allaah (Subhaanahu wa Ta’aala) says:
