Reference: Majmoo’ Fataawa wa Maqaalaat Mutanawwi’ah – Volume 6, Page 366
Question: What is the ruling regarding saying ‘as-salaam [‘alaykum] to someone on the telephone if you do not know whether they are Muslim or not?
Response: The ruling regarding that is the [same] ruling of when you meet [someone] and if you know him to be a disbeliever then he is not to be greeted with the salaam, however if you do not know, then there is no prohibition in that.
And with Allaah lies [all] success.
