Yes, I broke mine. Good and proper. Hey, I’m a mobile dev. If I don’t get to break a phone once in a while, I’m not doing my job properly 😉 Problem is, the X10 I have (had?) has only a virtual keyboard :/
So the first thing you need to do is install the PC Suite from Sony Ericsson. And then it’s straightforward: Tools > Phone repair. Simple.
The app will prompt further instructions; follow those (yes, you actually have to read the screen). And remember to press the BACK key while connecting the USB cable to the phone.
Of course, that doesn’t always work or solve ALL your problems. Sometimes you just brick it real good- like mine.