You can try to use Appium (iOS/Android) which is free and has a feature that lets you record actions, and run them through. However this only works for UI functionality and any standard Unit tests will still need to be developed the standard way (manually). As a note, Appium is new (~1 year old) so there may still be bugs (such as not running in iOS devices with Xcode 5.0.1 +)
I feel it's worthwhile to mention that appium doesn't require any modifications/additions to your android/iOS projects like a few of the other solutions I have found.