One can get music to play when someone calls by subscribing (for a fee) to a ring-back tone service that’s offered by his phone network. The service lets a phone user purchase a song and set it up to replace the network’s standard ring-back tone.
The exact procedure varies from network to network and phone to phone. For Verizon, one has to go to the Media Store online, search for the artist or track intended for use as a ringback tone and buy it. The Verizon Tones App allows a user to set a purchased ring-back tone as the default one.