Hi Elia.pimpy,
I assuming you can program Javascrip. chat,html is an example for p2p image transfer and chat functionality and currently we dont have an working example for conference.html but what you need to implement is very similar for conference room chat messaging.
If you check conference.html closely in AMS EE 2.1, you will also see that it uses webrtc datachannel to send mute/unmute and enable/disable video events to all other clients. Analogously you can use webrtc datachannel to send chat messages and images to all conference participants. Instead of sending these events, you will send chat messages. So if you merge the displaying chat mesages part of the code from chat.html with webrtc data channel messaging part of conference.html you will have all the necessary functionality.
Additionally, I will add a feature request conference chat messaging example but I am not sure when it will be implemented.
Best Regards,
Can