[geographomics]

There's no known API to read the UID out (there is one to use it, or the GID, or any other AES key: http://iphonedevwiki.net/index.php/IOCryptoAcceleratorFamily...), no published side-channel attacks, and the destructive/invasive techniques that would involve decapping the chip and using an electron microscope are not solid enough to use for this, such that there would a huge risk of destroying evidence.