Instantaneous Call Sessions over a Communications Application

In one embodiment, a method includes determining, by a computer server machine, that a callee-user is available for a communication session based on location information associated with a client system of the callee-user; sending, by the computer server machine, in response to determining that the callee-user is available, a notification to a client system of a caller-user indicating that the callee-user is available; receiving, by the computer server machine, a request from the client system of the caller-user to initiate the communication session; establishing, by the computer server machine, the communication session to enable a media stream comprising media captured at the client system of the caller-user to be received at the client system of a callee-user; and sending, by the computer server machine, the media captured at the client system of the caller-user to the client system of the callee-user.