In a telework scenario, the lack of informal communications, such as impromptu meetings, is a hard-to-solve problem for those who work at home over the long term. To facilitate informal communication, a system called media space provided an always-on audiovisual connection between distributed workers. Moreover, recent studies suggested that telepresence robots featuring audiovisual capabilities like media space are effective for informal communication. However, in practical use, various problems exist. Therefore, in this paper, we survey the systems of media space and telepresence robots concerning the advantages, problems, and solutions. We also discuss the unresolved issues and required investigations. One of the unresolved issues is that a stationary or desktop robot has a difficulty in initiating informal communication because it cannot move around the office. To tackle the issue, we introduce our experiment suggesting that a robot emulating the social greeting process actually promotes informal communication compared with no emulation.