I recently received display and touch glass from my friend´s broken phone Sony ST21i aka Sony Xperia Tipo and now I wonder if I can use it w/ Arduino UNO.
think you should search for a datasheet.
Are there any numbers on the device?
Can you post a picture of it?
Unless you can get a datasheet for it, forget it. Those kind of displays are made to order, and the spec sheet is not publicly available.
You also need to figure out how to connect to that tiny connector. If it's a high resolution display (more than 320x240) there is a good chance that the display has no built-in controller, and thus using it with arduino will be as good as impossible.
// Per.