No Sound

One of our iphone 4 has no sound.

Investigation into has brought me to the Airplay mode of the phone when I double click the home button and swipe to the left twice and hiot the Airply button. I see all the ATV devices in my house (4) but no option for the iphone itself as on my other iphones, instead its showing Dock Connector as the onbly other option, and thats why I am getting no sound whatsover. If I plug the phone to the dock connecter I get full sound.

Any ideas how to get the sound back to the iphone. I did a full restore and no cnhage there.

Thanks!