I am wondering if someone knows the best method for storing data in a global DB against a mobile device (iOS and Android)?
I am building an app that writes/retrieves
As of now I don't think its possible to get the hardware devices guid using air mobile. However you do have a couple of options.
If the MAC address is good enough for you there is an ANE that will let you grab it on both iOS and Android.
http://www.adobe.com/devnet/air/native-extensions-for-air/extensions/networkinfo.html
and an example of how to use it
http://cookbooks.adobe.com/post_Getting_NetworkInfo_from_both_Android_and_iOS-19473.html
You could also write your own ANE, it should be pretty simple to wrap both Android and iOS implementations.
Objective-c: [[UIDevice currentDevice] uniqueIdentifier]
Android: TelephonyManager.getDeviceId()
If your app requires any kind of user account or login the best option would be to store this setting in the remote db.