This just went live: Google Talk.
I already tried it with someone in NY (who made me aware of this, thanks, Ace).

Quite a few have written about this, too.
Looks like any other instant messenger, and I guess at the moment it is. It offers the regular features, including phone-like talk services. And, being real american, it has a typical clause at the bottom of the page:

Google Talk is not a telephony service and cannot be used for emergency dialing.

(Though I think the one from Yahoo! is even better: )

Emergency 911 calling services not available on Yahoo! Messenger. Please inform others who use your Yahoo! Messenger they must dial 911 through traditional phone lines or cell carriers.

So why download this? I already have 4 different messengers, that I combine in Trillian. This is already stupid, but I have no choice – but unfortunately, most of the people I know are on the known messengers, of which O’Reilly says

It’s an open standard–the big boys (Yahoo!, MSN, AOL) are notorious for pissing matches over interop that make MMS messaging on cellphone look like a W3C hot-tub party

The Google tool imports all my contacts from Gmail. That’s great, however I don’t have any contacts there, for the same reasons as above. I also didn’t need another Email provider…

They might achieve market dominance with this. But only, if the whole Jabber movement goes „AOL“ and covers wider segments of the online community.

However, this article says it’s rather about Google wanting to buy Skype.