From the gmail blog:

… today we’re launching voice and video chat — right inside Gmail. We’ve tried to make this an easy-to-use, seamless experience, with high-quality audio and video — all for free.

Say hello to Gmail voice and video chat

You must download and install a small bit of software from mail.google.com/videochat

… This is obviously a big jab at Skype. With VoIP and video chat functionality in Gmail’s familiar surroundings, many users will feel less need to ever use Skype. Sure, Skype’s client has a ton more options than Gmail’s simple video chat, but many users will prefer Gmail for precisely that reason. …

The Anti-Skype Arrives – Mashable