If you're paranoid about people listening in on your phone calls, the Tele-Safe II should provide you with some peace of mind. It can detect wiretaps and keep them from hearing anything, but let's be honest — no one is going to tap your phone to listen in on you ordering pizza. More usefully, it can detect when another phone is picked up elsewhere in the house and will mute their extension. Now your wife will be unable to listen in on your sordid calls with the Papa Johns guy. Privacy, it's a beautiful thing.
It's available now for an only-reasonable-to-the-paranoid price of $195.