What I used it for was to simulate the tones made when coins entered a pay phone so I could call friends for free. A recorded voice would say, "Please deposit $3.75 for the next three minutes." Then three minutes later a recorded voice would interrupt - usually my girlfriend and me, to say, "Please deposit $3.75 for the next three minutes." My girlfriend would say, "You don't have to put all that money in the phone, I'll call you back." I could never say, "Don't worry baby, I have a dialer," because Ma Bell was always eavesdropping; I could almost hear her breathing. So I had to let girlfriend believe I was generous with my coins.
Long before cell phones replaced pay phones the phone companies got better and better at preventing the use of the device. But I have kept it. Now, if not technically an antique, it serves the same purpose. It usually sits in my china hutch between Abe Lincoln's beard (or some such wad of hair) and my stuffed passenger pigeon, or carrier pigeon rather.