I found an interesting thing on the internet, called an iPhone/Android controlled helicopter, which works with an app, sending signals from our touchcreen phone trough 3, 5 mm audio jack to a transmitter and on to the chopper.
This is the app (below), but I'm not sure which android smartphones does it support. I mean, shouldn't it work on all of them?
https://play.google.com/store/apps/details?id=com.uprtek.rd2.icontroller.udi&hl=sl
>>> Mobile audio jack transmitter?