I'm curious... what are some of the games or apps which require both an iPhone and an iPad? For example, the drawing app Remote Palette lets you connect your iPhone and iPad via Bluetooth, so that you can then pick colors from your iPhone to draw on the iPad canvas. Another example is PadRacer... Edit: Found another one, "MPad Controller" for several games...
The Incident uses the iphone to control on ipad. Scrabble uses iphone for tile rack This one dont count but Trench run has a thing where you use iphone to control on the computer.