Yes, It is correct. You can call virtually any phone number in the world using gTalk with the help of some third party service. Google itself is working on this and hopefully you will be able to make high quality cheap phone calls using gTalk. Till then you may use third party providers for making the calls. Some of the gtalk to voip service providers are: gtalk2voip.com, gTalkPhone and Splinter.net etc.

Now as the title says, you may make free calls to test these service provider:

In order to make free phone calls follow these steps. I am going to use splinter.net service in this example because it is cheap and you don’t have to fill registration form to use there service:

Add service@splinter.net as a friend in your gTalk. You must use gTalk in order to use VoIP service.
Then after few seconds your request will be accepted by the splinter bot. Now send a message to this contact in this format ”call 1-801-806-0551″ and you will get an incoming voice call from them. Accept this call and you will be able to talk to the phone number you just entered.
They give small amount for testing the service, but because of low call rates it is enough to make few calls.
You may check the cost for the call to any particular phone number by entering the command: “cost 1-801-806-0551″ where 1-801-806-0551 is the US phone number in international format.
You may check the balance and add paid credit to your account be entering command: “MYPAGE” and opening your custom account page.
That’s it. It is easy and fast way to make few free calls to your friends.
The procedure is bit similar for gtalk2voip.com and gTalkPhone. Visit there homepages for more information

GeekLord’s comment: Although the voice quality is not up to the mark and I experienced considerable lag time while testing these services, The Google may improve it further and once again pose a tough competition for other such service providers like Skype any Yahoo! in VoIP field.