Ok I had been working with unity for about 8 months now and I have installed succesfully many builds to my LG Optimus Black (I know a little old)
Right now I’m working with Unity 4, have installed some builds (even networking builds) on this device, last time I had the same problem “application not installed” translated the code from JS to C# and it ran without a problem.
Now I tried the same (its a basic WWW + Start server code) and I can install it in 3 other (friend) android devices but it wont install in mine.
Got Android 2.2.2 (if that matters)