I just came across an interesting kickstarter project which uses your smartphone as the autopilot for your drone. Althogh its a great idea in concept I feel that most of the time its better to use dedicated hardware and separate camera. However although this phonedrone looks cool, I dont see much use in having a non stabilized downwards facing camera.
Other smartphone powered drones
Otherwise this idea is not that new, back in 2007 Christ Anderson (CEO of 3DR) build his first drone using windows CE, which used thermopile sensors to keep the aircraft level, and an iPaq 6515 Window Mobile phone for control and GPS. I also shared a post a while back about androcopter, an android powered quadcopter.
More recently in 2014 aeracoop created an instructable post on how to build the Flone, a smartphone powered miniquad.
And hte most recent smartphone powered drone comes from engineers from the Upen GRASP lab at CES2015. The main cool feature of this drone is it uses qualcoms vision processing library to do some cool things.
At the end of the day, do you think smartphone powered drones have a place? I tend to lean towards teh idea of augmenting your drone with a smartphone to do other tasks such as vision processing, or HD video streaming etc as its usually more reliable to have dedicated autopilot hardware.