I have been experimenting with the related Google Voice and the Google Call technologies. I really like them. For example, I see real potential for them to help teachers keep in touch with their students without having to give out personal phone numbers.
With Google Voice, I can set up a telephone number for free and configure it to forward the call to other phones. Or if the person leaves a voice mail, it sends me an email with the option to play it or read a transcription of it. (The transcriptions aren’t always 100% accurate and sometimes they can be funny!)
With Google Call, I can use the chat feature to make free out bound calls to real telephone numbers.
In combination, Google Voice and Call lets me take incoming calls through audio chat when my Gmail account is open!
Here are three quick tutorials about using the tools: