I am not as happy with AT&T's Unified Messaging, which I am also using. It is connected to my home phone line and will be disconnected as soon as Google Voice can replace it.

What I like most about both RingCentral and Google Voice is their shared ability to ring multiple phones in an attempt to find me. I also like being able to screen calls by listening to an incoming voice message while it is being recorded, and then answer if I want to.

I used to do that with an answering machine and the Google Voice/RingCentral feature is only slightly less useful as you have to answer the call to hear the caller leaving the message.

Google has recording features--sure to be used in ways people will regret--that RingCentral lacks as well as speech-to-text conversion. GVoice also allows specific greetings for specific callers.

The ability to turn voice messages into text and deliver it as e-mail is a Google Voice feature that many people are going to find useful, and something else RingCentral lacks.