Inability to call or text with Samsung Galaxy S3
Take a backup of your phone and do a hard reset.

Steps for a hard Reset


Turn the phone off.
Press and hold VOLUME UP and Home(center) button Press Power until
the phone vibrate Wait until you see the Android   logo then release
all the buttons
Select Wipe data/Factory reset with VOLUME DOWN, press Power (right
    hand-side) Select YES -- delete all user data with VOLUME DOWN and
    then press Power After format,    press Power again to reboot phone.
    (select reboot system now)


Source