I made some hacking and now I can also receive and send group messages with telepathy. They are just "converted" to normal messages. As a negative side they also show up in the phone book as normal contacts, but it doesn't bother me too much.

This is still far from ready, Android app is needed for sending/receiving pictures etc, but at least I can get reliable notifications of messages.

Here is my github branch with the group message hack:
https://github.com/TemeV/telepathy-m...SailfisOsHacks