Users of various devices may participate in communication sessions, but only if the interfaces and components of such devices feature a minimum set of capabilities involved in the communication session type; e.g., in order to participate in a teleconference, the device of every user has to be capable of sending and receiving audio. Instead, a communication session server may automatically convert session items received from each user into interface-specific representations for each other user, based on the capabilities of the interface and device of the other user. For example, speech recognition may transform speech to text output; speech synthesis may transform text input to speech; and video recognition may identify individuals and gestures in a video stream and represent this information as text. The server may therefore host a “mixed” communication session, where each user may fully participate irrespective of the capabilities of the chosen device and interface.