Russian design studio industrialdesign.ru sent this interesting design for a small analog thumbstick for mobile phones and other small devices. The clue is the telescopic stick.

You would push on the stick and turn it slightly to extend it from the surface of you phone (see images).
Now you can play games or navigate on your device more conveniently.
There actually snap-on plastic joysticks for mobile phones, but an integrated solution would definitely be better. Now the designers Yurii Elshin and Alexander Sekirash just need to find a mobile device maker to actually build phones with Compact Analog Thumbstick.
More details on the industrialdesign.ru site.