Smart one would control and allocate appropriate resources to app developers to keep the device running smooth and properly as an enjoyable overall user experience. For example, allowing music apps like Pandora to run in the background while the device does other tasks like email, spreadsheets web browsing.
A dumb phone would put no limits and have stupid things like running two videos at the same time on a 4" screen. Thereby depleting RAM and locking up the device or causing applications to be forcible close. Causing battery pulls and hard resets. (see playbook)