Same here....noticed it more with SMS, but I guess it could've been with a few calls I've missed too. I don't really know...but I can confirm the SMS issue.
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"Blondes may have more fun, but Edward prefers brunettes."
Mine as well, but if you change ringtone (that is ringtone and not SMS tone) to a different tone to force it to play and then back to the one you had set, then ringtones and sms work again for a while, but eventually they go silent again.