1. A method for operating a first computing device, the method being implemented by one or more processors of the computing device and comprising: receiving, from a second computing device, an incoming call to initiate a voice-exchange session; in response to receiving the incoming call, determining a message identifier associated with the second computing device, wherein the message identifier is determined based at least in part on data provided with the incoming call; in response to receiving the incoming call, prompting a user of the first computing device to enter user input that instructs the first computing device to handle the incoming call by composing, while not answering the incoming call, a message to a user of the second computing device; and responsive to receiving the incoming call and the user entering the user input, automatically addressing the message to the second computing device using the message identifier determined from the incoming call.