Google decided to use Jabber as the backbone. That means you can IM Google Talk users with any Jabber client using their Gmail address as their username. You can even do so using iChat. If I gave you a Jabber account for godlikenerd.com, you can use that as well. Update: Or not. I can’t seem to connect to chat via anything but a Gmail name. That’s not cool. According to Google:
It isn’t possible to call or chat with non-Gmail users through Google Talk (but we’re working on it). You can email any of your contacts by clicking the envelope next to their names in your Friends list, but if you want to talk to your friends live, they need to be Gmail (and Google Talk) users too.
You can invite your friends who aren’t Gmail users to download Google Talk. They’ll receive an invitation to create a Gmail account at the same time. Just sign in to Google Talk, and click ‘invite’ next to your friend’s name or click ‘Add friend’ at the bottom of your Friends list. Then follow the prompts to email an invitation to his or her email address.
The bad thing is that Google’s official client (the only one with VoIP capability) is currently Windows only, though Mac and Linux versions are in the works. VoIP for those not in the know, is Voice Over Internet Protocol, otherwise known as phone on the Internet. Skype has recently made this service particularly popular, offering such options as voicemail, external phone numbers, and the ability to dial phone numbers. Google Talk still lacks this apparently.
This extra weight may push a lot more users to Jabber, which benefits us all (due to its decentralized nature, there is no reliance on a single body). Heck, it may push the major players (AOL/ICQ, Yahoo, MSN) into opening a Jabber interface into their services. I wouldn’t hold my breath though.