On Call is a GTA Online gameplay feature that allows a player to continue playing Free Mode while they are queued for a job. It is available via Quick Job through the phone. The player will be able to play Free Mode until the mission they are queued for is launched. A timer will appear in the bottom-right corner of the screen displaying the amount of time a player has been waiting for the job to launch.
Strangely, if the player is listening to the radio in a vehicle, and keeps searching for jobs to join while on call, the song on the radio will change, upon exiting on call, it will change back to its original song, though going back into on call will result in the song changing again. This is probably due to on-call searching through different GTA Online lobbies, which have a different ordered tracklist, resulting in the radio changing to the appropriate lobbies song.