A teacher could play both roles but it can get very hectic. All conversation then flows around this point for 15-20 minutes. Time is then allowed for people to scroll and read what has been posted, the some more comments and questions can be added. The speaker then introduces the second point and the process begins again. When they leave after a few minutes, then another person can ask to join in.
Primary students chat with the characters of a book they are studying.
Pre-service teachers, senior students or adults who are familiar with the novel could step into the role of the characters and make an interesting chat with students. On several occasions I have made great use of the IRC server that Roy Kennedy hosts. Andy helped kids experience the process he goes through as he writes his outrageous stories. The author Jill Morris did a book discussion with students and was most surprised by their detailed knowledge of her works and their clear opinions and reasons for their likes and dislikes. These were ideal ways to use synchronous technologies with primary students.