How open is Android for developers?
<p>Long story short: How open is Android OS for developers?</p>

<p>A little in depth:<br>
For instance, if I'm willing to write my own text-input interface, would it be possible (like, totally overwrite the built-in-phone one)? Or that's something like core feature and cannot be changed?</p>

<p>And, is there a difference for developers, whether I buy a Google phone, HTC or Samsung etc.?</p>

<p>P.S. If that's all possible, no warranty voids for such changes?</p>

<p>Hope I've made myself clear and thanks in advance!</p>
