Communicator 7 - Can I do a conference call when using VoIP?

You can do what is called "3 way calling" which will allow you to add 2 people in addition to yourself to a call. 

If you require more people to join a call you will not be able to do this from your phone or the Communicator 7 application.  You can call any regular phone number (even outside Dentistry) to add them to the call, they do not have to have a VoIP phone.