It's hardly an illogical next step for the service, but that doesn't make Google's introduction of free calls from Gmail to US and Canada phone numbers any less of a big deal. Call from Gmail, as the feature is dubbed, not only gives US users free calls to residents of their own country and northerly neighbours, but also facilitates cheap VOIP calls internationally, using pre-paid credit purchased from Google. It's at this point that Skype and its ilk need to be concerned.
International landline calls are being charged at $0.02 and up, so if you can keep your conversation under a minute, you really can offer your "two cents" on any given issue. Mobile calls will, unsurprisingly, cost more, but will almost certainly still be cheaper than using your 'real' phone to make the same call.
The significance of Call from Gmail is not, obviously, that Google is offering voice over IP telephony - that's hardly a revolutionary communication medium. Rather, it's the tight integration with Gmail - and by extension Google chat - and Google Voice. Those fortunate enough to have Google Voice accounts will be able to accept incoming calls via Call from Gmail, making it even more frustrating that the UK isn't able to get access.
The free calls to US and Canada landlines are being offered until the end of the year, so if you are a US citizen now is the time to give Call from Gmail a go to see what you think. Hopefully if the American-based pseudo-trial period goes well an international roll-out won't be too far behind.