There are two different topics. One is the problem of sending bulk SMS to e.g. a group of parents and the other one is group messaging where everyone sees everyone else message. They both are obviously valid requirements.
So far we have worked on the bulk part of it; as we see users starting to use it we will have to address the problem of transferring conversations around in the team, similar how you would transfer a call.
As for the group chat, we actually had that in the early plannings. However in the real world, as of today, it seems most users don't use the PBX for such group chat. This is the world of the mobile phone chat apps, including iMessage and Android Messages that do that job very well.