Conference calls
There is a service called InConference that turns your extension into a conference room which makes it very easy to set up conference calls. You can also make group calls from your extension.
Information about Inconference
It makes its very easy to hold a conference call, and the only thing that participants need to know is your phone number and possibly pincode.
You arrange a conference by referring your extension to the CMG web.
Groupcall
You can make group calls from your extension with a maximum of 8 participants.