Google is beta-testing a new free service called Google Voice that builds on their existing GrandCentral technology.

Google Voice offers one number for all your calls. That means you have one number that rings from all your lines -- no need to give out a home number, an office number, a cell number etc.

In addition, Google Voice offers free calling, voicemail, conferencing and more. There are no monthly fees, no minimums and no sign-up fees. As always, this service is likely to be monetized with ads going forward.

With the voicemail feature, you're also able to listen in as voicemails are being left and pick up in the middle of the call -- just like you would with an answering machine. You can also have voicemails automatically converted into a text message.

But the real market disrupter here is the free conference calling. Companies pay big money for this, and here Google Voice has it for nada!

The service is currently only available to existing GrandCentral customers, but you can also sign up to be notified when Google Voice is fully launched.