Methods and systems for allowing users to participate in concurrent real-time audio or audio-video communication sessions over the Internet, the public telephone networks, and other networks. A user may switch among two or more conversations, and upon doing so, can play back the conversational content that was created while the user was engaged in other conversations or other tasks. After playing back part or all of the new conversational content, the user can reply with an audio or audio-video instant message that can then be played by the other conversation participants. Temporary storage of the conversation content (the instant messages) can occur on network servers, on the sender's terminal or on the recipient's terminal, depending upon preferences and the capacity of the terminal devices.