Besides flashing the zip from the previous you will need to reactivate it! there is a post here already with the same exact problem where i explained how to do it.
Edit: Here are the directions on how to do it.
If i remember correctly you used Gogglevoice at one point and then reinstalled VVM!You may need to re-activate you VVM. I had to do the same thing it is very simple! Let me fine the directions.
Know what to do if you are not receiving your Visual Voicemails
Steps you can try if you are not receiving your Visual Voicemail messages:
1. On your phone keypad, enter *38 and then press Talk to cancel any call forwarding(When you use Goggle voicemail you
are actually forwarding your call to them, this call will only be about 5 sec and then will hang up by itself)
2. Power off your phone, remove and reinsert the battery and then power it back on
3. Update the data profile on your phone; go to Menu > Settings > System Updates > Update profile
4. Go into the visual voicemail application and compose a visual voicemail message by selecting Menu and then Compose. Make sure your message is longer
than 15 seconds and send to firstname.lastname@example.org.
You can find these steps buy going to Voicemail->settings->Help->Scroll to Most-Viewed topics ->Know what to do if you are not receiving your Visual Voicemails