> How can they know/figure it out? Sony's answer for Xperia phones used to be that you'd unlock the bootloader with a key you got from them by entering the ser

> How can they know/figure it out? Sony's answer for Xperia phones used to be that you'd unlock the bootloader with a key you got from them by entering the serial number/IMEI. As part of that, they warn that using custom ROMs that damage the phone - by overclocking, for example - would void the warranty. It's a reasonable compromise, in my opinion.