I would like to be able to take an older smartphone and use it as a smartcard-like device but with a full-fledged computer on it. For example, being able to use a Motorola Droid with a USB cable as a password manager. Keep the key secured on the SIM card. Use the touchscreen to enter the unlock password, and choose a password off a list. Send the password to a computer over USB by emulating a keyboard, or a custom driver that creates a secure channel to a specific app for authentication.