I know that this is a somewhat old post, but just in case someone new is looking for this information, I was able to get my voicemail indicator to work perfectly. The key is to log into your google voice account, go to "settings", then "calls", and under "missed calls", uncheck "place calls in inbox". I did this and now my light works exactly as it should. There's a slight lag between the message arriving or being deleted and the light changing, but it does work.