....so they, the company, in this case, Lippincott Industries Inc, had the phone company install different ringers in the phones, so that certain numbers would generate frequencies matched to a particular ringer? something like that!!!??? Well, the phones, mostly 554 SC and ITT, which has most, if not all SC internal parts, are NOS, and all from the 70's. I paid $125 for the lot of eighteen, and installed ringers in the 500 and 554 LIME GREEN SC phones, and sold each for $75, so I made my money back already. kept one SC LIME GREEN for myself. don't see many of them around!