&gt; though it&#x27;s pretty darn impractical to do at any kind of scale.<p>How so?  It&#x27;s a solved problem.  Don&#x27;t smartphones already have numerous device-specific identifiers and keys loaded to them?  All they would really need to do is slap an extra sticker on the device with the device-specific key printed on it.  For instance, my phone came with a sticker with its IMEI printed on it.