First of all, THANK YOU everyone for taking some time to answer every question. I really appreciate it. I have been reading, and reading for hours...my eyes are starting to bleed.
So... there is NO WAY we can get a better Android than the 2.3.5?
My build number says 4.5.1A_SUN_USC_19.0, that means I cannot unlock the bootloader, isn't it?
Is there another way (hack?) to improve the performance of the cellphone? I have root it, just to change some files I couldn't, e.g. the sound of the camera.
And finally... is it THAT bad being stucked on 2.3.5?