The type and angle of the display can be important because you read the display fleetingly while you're speaking. Before buying, see how well you can read the display in the dark and in a brightly lit car. Most car-based phones are speakerphones, which allow you to keep your hands on the wheel while speaking. Making a call can be dangerous, particularly when in traffic. The function key accesses most of the carrier-supplied services.
Most phones have security features that block outgoing calls to certain numbers without a password.
Cellular phones have volume controls for the ringer, keypad tones, function and alert beeps, as well as a muting feature. Many features are accessible through a menu listed on the display panel. Because securing the handset is an issue in a moving vehicle, there is wide difference in the ease or difficulty of removing or replacing the handset to and from the cradle. Some require a button or latch be pushed to release the handset, a method paradoxically called quick-release latches. To return the handset many phones need maneuvering into place, others use a magnetic seal.