I have asked the same question many times to many different people and all of them have told me no that there isn't a way to stop the duplicate notifications. I find it very annoying, but I guess they just really want you to know that you missed a call
This may be a fix. Are you getting a message in your email box about the missed call? Or about the voicemail? If it is the missed call follow these steps.
1. Press the send key
2. Press menu then select options.
3. Scroll down to "Call Logging"
Once you click on "Call Logging" you should see 3 options. Missed Calls, All Calls, And None. Select none and it should take all call logs out of your mail box.
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