Samantha is Earthbound - S8-E16
Other mistake: This episode is a repeat of Season 4 No Zip in My Zap with the better Darrin 1. Since Samantha previously became earthbound for not practicing her normal, day to day, witchcraft. They would know why Sam is again earthbound. And, Samantha constantly uses her witchcraft.
Answer: Telstar was an early communications satellite system. Darrin, in a particularly sexist manner reflective of this era, is saying that telling a secret to a woman means it is guaranteed to be "broadcasted" to multiple people.
raywest ★