I have found a solution from Google.
Don't use your Ooma phone number as your main phone number, use Google phone number instead. Go to http://www.google.com/voice to create your own phone number (it is free). Then forward call to you Ooma phone number, anyone leave a message, Google will send a voice mail notification to your email. All these great features (call forward, voice mail notification) are free from Google. Good luck.
New VM email notification not working anymore
Re: New VM email notification not working anymore
By the way, you can call US and Canada for free from Google. For Omma US is free call but Canada is not.