My home phone on SP1 using GV blinks there is voice mail and does the double tone thing saying there is VM where there isn't. I call GV voice mail and it says no new messages but the phone is blinking, VM it lit up and double tone.
I get email notificaiton on missed calls, voice mails ect ok - just the phone says there is VM when there is or isn't.
Not a huge deal - but annoying.
Make sure missed calls are not being sent to your Google Voice Inbox.
Log into your Google Voice account and delete everything in your Inbox if it's not empty.
If you still have a VMW problem, see the second part of this post:
http://www.obitalk.com/forum/index.php?topic=2054.msg12985#msg12985