1. A method comprising: at a computer system including one or more processors and memory storing one or more programs for execution by the one or more processors, the one or more programs including instructions for: automatically without human intervention, determining whether a handheld electronic device is not in use; upon determining that the handheld electronic device is not in use, automatically without human intervention activating a microphone associated with the handheld electronic device; obtaining ambient sound using the microphone; determining a first context of use of the handheld electronic device; determining, at the handheld electronic device, a first noise profile based at least in part on the ambient sound, wherein the first noise profile is configured to enable the handheld electronic device to at least partially filter other ambient sound obtained at a later time when a voice-related feature of the handheld electronic device is in use; storing the first noise profile in association with the first context of use, wherein the first noise profile is one of a plurality of stored noise profiles each associated with a respective context of use; receiving an audio signal including voice and background sound; determining a second context of use of the handheld electronic device; determining whether the second context of use is substantially similar to the first context of use; upon determining that the second context of use is substantially similar to the first context of use, selecting the first noise profile; and using the first noise profile to at least partially filter the background sound from the audio signal to obtain the voice.