PC-to-PC calling can only occur between two people. The magic number is two. If you and a friend are on a PC-to-PC call, the Open Talk link will be clickable by friends on your Messenger List. However, they will not automatically be connected to your PC for a PC-to-PC call. Because you are on a call with another party, you will have to choose to accept or decline the call (or IM only). Accepting the call will automatically place the first (current) call on hold and start the new call. If you decline the call, the new call will be sent directly to voice mail.