Two people on opposite sides of the country fall in love without ever meeting: a widower’s son calls a radio show, and the father’s voice is heard by a woman engaged to someone else. On this almost impossible premise Nora Ephron built her 1993 comedy with Tom Hanks and Meg Ryan, whose leads spend nearly the whole film apart. Tomorrow Theater is showing it the weekend after Thanksgiving, alongside “Mystic Pizza,” “When Harry Met Sally…” and “Moonstruck.” A good excuse to step away from the holiday table and remember how romantic comedies used to be made.