Hello Sunshine is the app to shine your day. It will say Hi ! everytime you take your phone !
This is the great app designed for the XKCD phone ( http://xkcd.com/1363/ )
Launch the app, start the background service (a notification tell you it is running...) and forget it.
Then, everytime your phone sees the light (when you take it out from your pocket for example), it will tell you "Hi !".