In a recent post on his blog, Thanassis Tsiodras has an impressive tale of his Android hacking adventures. Wanting to run Debian from chroot, he ends up customizing the boot image; attaching a serial logger to the headphone jack; and intercepting the over-the-air update image to control the boot process.
At last, it seems he achieved what wanted, but of course at an extremely high price. Most mobile devices are now very hostile towards any other use than was is dictated by the manufacturer and OS vendor. Thanassis ends his article on a sober note, saying that once even this hack is secured against "Android might as well be called iOS".