It should come as no surprise to anyone that Google is completely focused on Google+ and they plan on integrating it with every one of their services that they can. Today Google has announced that they have integrated your Google+ circles into Google Voice so that you can easily manage your contacts and how they are able to reach you.
Calls from your “Creepers” circle can be sent straight to Voicemail, only your “College Buddies” circle will hear you rap your voicemail greeting, or you can set your “Family” circle to only ring your mobile phone.
Setting this up is extremely easy, just head into your Groups and Circles tab in Google Voice and customize it the way you prefer.
Source: Google Voice Blog