Q. What should one do when he picks up the phone on a Friday afternoon and, to his horror, discovers that the caller is a non-religious Jewish family member who is now in a part of the world where Shabbos has already begun (or might have already begun – as sometimes one is not sure)? Should he hang up immediately on the person who is calling? Is one is asked a question by that person, may he answer the question?

A. Piskei Teshuvos (246: 7) permits one living in a time zone where Shabbos has yet not started or has already ended, to phone or to contact on line a Gentile that is actually on a time zone where it is Shabbos and instruct him to do prohibited melochos. Horav Shlomo Miller’s Shlit’a opinion is that it is prohibited. However, all agree that he certainly would not be permitted to cause or help a Jew to desecrate Shabbos in the place he dwells, as he would transgress on the prohibitions of lifnei iver (placing a stumbling block in front of the blind) or at least on helping someone commit a sin, even if he is not a religious individual.
Therefore Horav Shlomo Miller Shlit’a advises to just curtly say it is Shabbos and will contact latter and then hang up.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a