On Friday at 4 o’clock my son called me. At the end of our conversation he said “Good Shabbos, Abba”. Having read this thread and being determined to be a good Jew, I told him he could not hang up the phone. By Motzei Shabbos his hand was very tired and his wife and children were annoyed.
Lesson: Judaism permits the use of the brain before reaching far-flung and quite impossible halachic conclusions.