Device ID for Android and iOS

I believe there are a few similar posts, but none that I can see with a straightforward answer.

Basically, what's the best way to determine a device identifier from AS3/AIR from which an app is opened? It looks like this is possible on BlackBerry Playbook (http://www.blackberry.com/developers/docs/airapi/1.0.0/index.html) through the qnx.system -> hardwareID property.

Is there something to determine a device ID for Android and iPhone? The goal is to allow a user to upgrade from a Free version of an app and retain all of their scores/username information (which are stored in a remote MySQL database and fetched via URLRequest) in the Full version. Since there are no passwords/unique ID's involved (other than their username), it appears that they will no longer be linked to this account if they upgrade the app (which is technically a different application). Of course, if they upgrade their phone it will no longer be linked to that device (which is fine in that case).

Are there best practices or alternatives for this type of procedure? Apologies if this has already been answered elsewhere; I browsed most of the forum without much luck.