I have not seen this posted anywhere but if you push the mute button on the top of the phone, it will mute and unmute(or start and stop) your music while it is playing in the background. I know if you hold down the mute button for a couple of seconds it will also put the phone in standby mode as well. Simply tap the button and your music will start playing. Always wondered why there was a mute symbol on the button. Now you know.

If you are using a wired headset (with a mic) to listen to your music you can press the button on the mic to mute the song playing too. Do it all the time.