Voxli.com which is currently on beta running gives instant voice conference facility; all we need is latest browser with flash player plugin.
As we know Voice chat through IM work fine, but Voxli.com is really focused on giving simple solution for different group of users. To start a voice chat conference is as easy as clicking a button, and share the URL with anyone who wants to participate. Voxli.com supports up to 200 people at a time without any custom software installed, and compatible with Windows and Mac. The service even enables push to talk control when you are speaking even if you are outside the browser.
Voxli.com will be useful for making voice chat while playing group games or simply engaging in conversations as large groups.