Support Help re messaging/notifications

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http://androidforums.com – About a fortnight ago I noticed a little symbol in the top corner of the phone a circle with an i in the middle and crossed through, like a no entry sign and since then I cannot get my messages or email notifications to make a sound, all my tones are on but i only know i have a message if the LED is flashing, anyone know what to do to resolve this? Reesh (General)