A method of facilitating participation of a WebRTC enabled terminal in an ad hoc conference or chat session hosted in an IP Multimedia Subsystem (IMS) network, where there is an ongoing session between first and second terminals using the IMS network. The method comprises sending a link from the first terminal to a third terminal that is not provisioned or not registered with the IMS network, where the third terminal is said WebRTC enabled terminal and the link provides access to a conference/chat-correlator identifying said ongoing session, and sending a session invite from the third terminal to the first terminal, via a WebRTC gateway, WGw, the session invite including the conference/chat-correlator. The method further comprises, at the first terminal setting up a second session between the first terminal and the third terminal in response to the received session invite, and at the first terminal using the conference/chat-correlator in the received session invite to associate the ongoing and second sessions, and joining both sessions into an ad hoc conference or chat session hosted in the IMS network.