Airplane mode (also known as aeroplane mode, flight mode, offline mode, or standalone mode) is a setting available on smartphones and other portable devices. When activated, this mode suspends the device's radio-frequency (RF) signal transmission technologies (i.e., Bluetooth, telephony and Wi-Fi), effectively disabling all analog voice, and digital data services, when implemented correctly by the electronic device software author. When cellular phones became prevalent in the 1990s, some communication headsets of aircraft pilots would register an audible click when a cellular phone on the aircraft would transceive a signal.[citation needed] This clicking on the headsets became overwhelmingly distracting to airframe control, with more and more phone calls from airplane passengers as time went on.