The voice-enabled IM service actually went live on Tuesday afternoon, according to blogger Ben Guild, who was able to log on around 5:40 EDT.
The new service marks another step on Google's evolution from search service to Internet gateway.
The free Google Talk service lets users initiate text or voice chats from a stripped-down interface. The service is integrated with Google's free e-mail service, Gmail, so that, when a Gmail user downloads the IM application, it's instantly populated with that person's Gmail contacts.
''All Google's competitors have this kind of capability or are developing it; maybe out of necessity, Google needed to develop IM and VoiP,'' said Kelsey Group analyst Greg Sterling.
Yahoo Messenger launched a PC-to-PC voice chat feature in 1999. In August 2005, it launched Yahoo Messenger with Voice, which is based on SIP and includes voicemail. AOL launched a consumer version of its AIM Voice Conferencing service in December 2004.
Sterling said it was natural for Google to combine IM and VOiP, but interesting that it tied them into e-mail. ''If you adopt this, you need to sign up for Gmail, which will drive Gmail adoption as a byproduct of the popularity of this,'' he said.