I have a home telephone cable on my car but I dont know what it is for.. it came with it.. can someone help me

After I bought my car i noticed it ha a home phone cable by the visor, i wish I could know what it was used for or what uses can it have.. THANKS|||It is for a radar detector. Probably a Valentine 1, that is what I have. It is called hard wiring, where a cable is run up the car to around the visor/rear view to power a radar detector stealthily. Plug one in, I bet it would work.|||It might be for a garage door opener.|||It could be a connection for a VERY old car phone.