Until s screenshot was discovered by a Googling Google reader, an official Google Talk feature that would let you make real phone calls from the client could only be speculation. In this Adobe Breeze presentation, during the "Google Talk" section, you will notice a screenshot that doesn't quite look like anything available in the client as it exists today -- links that say "Show dialpad", "Call details" and "Close".
I don't know why else these would exist in an official Google presentation unless the feature is being internally tested. It's not too crazy to assume either -- General Manager of Google's Enterprise division, Dave Girouard, hinted at it in an interview with internetnews.com back in December
Girouard said that Google Talk, which currently allows users to make VoIP calls among themselves, will be beefed up to integrate with traditional phone systems as well as VoIP offerings from other vendors.