Update for Google Voice has faster notifications
Google Voice is one of the most popular Android apps, as it has calling integration, voicemail transcription, and text messaging. Despite it's usefulness, one major complaint is that by default it would take 15 minutes for voice message notifications to show up on the phone, unless you changed the polling frequency to less time, but as a result it would use more battery. With the new update for Google Voice this week, the app now uses push inbox synchronization, so new messages show up in only seconds, and also uses less battery power. Also with the update, Google Voice will automatically disable SMS forwarding to your mobile phone, so you won’t receive duplicate notifications. The final part of the update is that it is now faster to interact with your contacts from the Google Voice app, as you can click on any contact's photo and get the option to quickly respond to voicemails by either email or IM.
source: Google Voice Blog