An architecture for a contactless smart card or payment device, where the smart card is intended for use in both commerce transaction payment and transit fare payment (or other venue access) environments. The payment device may function as both an electronic wallet for commerce transactions and as a transit system card, for access to and fare payment of transit services. Implementation of both functions may be achieved by use of a dynamic memory management system that permits data for both the payment and transit applications to be stored on the card, with the transit data and storage locations isolated from those used to store data intended for use in paying for commerce transactions. The transit application specific data may include access control data (keys, passwords, identification data) or data required for fare calculations (rates, historical data on system use), for example.