How To Automatically Mute Music When Receiving VoIP Calls [PulseAudio]

By default, in Ubuntu and probably other Linux distributions, if you're playing music in Rhythmbox, Audacious and so on while receiving a call in applications such as Skype, Ekiga Softphone, SFLphone VoIP Client and other VoIP applications, the music continues to play even after answering the call. PulseAudio has a feature that allows pausing or muting the music when receiving a call, but it's not enabled by default, at least in Ubuntu, so here's how to enable it.