The process of setting up a Bluetooth network is referred to as “pairing” because the network consists of only one “pair” of devices. Although it is often possible to pair one device to multiple other devices, each connection is secure and unique.
To pair a cellphone to a car stereo, the phone and the head unit must be Bluetooth compatible.
Most car infotainment systems offer Bluetooth connectivity, which allows for seamless hands-free calling. This same functionality is also offered by both aftermarket and OEM Bluetooth car stereos, and you can add it into older systems with a hands-free car kit.