Kyocera K500 User Manual page 60

Check to see if you have barred incoming calls.
10. SMS messages are not sent.
Check the Message Centre option in Message Setup menu.
11. Audible key tones are muted and all audible alerts are changed to vibrator alert.
Check to see if your phone has the Silent Mode function on.
12. If some menus relevant to the sound are not visible on the Sound Setting menu.
Check to see if your phone has the Silent Mode function on.