Avaya EU24 1XU-A Key Expansion Module (700381817). The Avaya EU24 1XU-A Key Expansion Module is an optional device that extends the number of call appearances and Feature buttons available on the telephone. The Avaya EU24 1XU-A expansion module has 24 buttons arranged in two columns. Depending on how the Avaya EU24 1XU-A Module has been programmed for your call processing system, these buttons can be call appearances, which are lines for incoming and outgoing calls, or features like Call Forwarding.