I don't know what I've modified recently, but my Samsung Galaxy SII (running stock Android 2.3) keeps notifying me vocally whenever I get an incoming call or an SMS.
Is there a way to disable this feature?
Look under SETTINGS > ACCESSIBILITY for Talkback or something similar. Also check under settings of individual apps - Phone/Dialer and Messaging.
Finally check to ensure that DRIVING MODE has not been recently enabled. That might also be the cause. Look under SETTINGS > VOICE INPUT