In a smart card system in which applications executing in different execution contexts are allowed to communicate with each other only through shareable interface objects (SIO's), a registry mechanism is provided to mediate in inter-application communication between legacy applets, extended applets and servlets. A request by a client application for a SIO of a server application in a different execution context is routed to the registry mechanism by the system. Dependent on what types the client and server applications are, the registry mechanism provides call interfaces as would be expected by the applications to enable passing the SIO from the server application to the client application. In one embodiment, servlets and extended applets may also register and unregister their SIOs dynamically with the registration mechanism.