Yes, this is awesome, I just figured this out the other day.

It should be noted, though, at some point the outgoing call point may become not free.

http://www.grandcentral.com/support/showanswer/605 says:

"Will GrandCentral always be free?
Our current plan is to offer a free service with as many features as we can and later add paid features at a very affordable prices. During beta, all available features are free."

Also, from the FAQ:

"Will GrandCentral always be free?
Yes, we're excited to say that we will always offer a free version of GrandCentral, even after beta. Our free version will include unlimited inbound minutes, unlimited voicemail (up to 30 days old), and access to all of our core features. During beta, we're giving everyone unlimited access to our premium features. In exchange, all we ask is that you send us your feedback (good or bad) to beta@grandcentral.com. We'll read every comment."

However, it is Google now, and you know how long their betas generally last. So you may be able to enjoy the free outgoing calls for a long time, who knows?

-SG