I've just buy a Motorola Defy plus.
It's a great phone ! No more important call missed.
So i can give the xperia to my one year dauther who loves to play with. It's allready old, the glass is broken, volume buttons does not work, and battery is down.
It's a cool end of life for him !
All informations to build boot.img from scratch are in the first post of this thread. I hope that someone else will continue. All sources are public.
Anyway, it's now usable as a phone (if not at end of life like mine).