I don’t recommend that you *always* return true. This would tell the Android OS that you’re overriding *all* keys. For example, pressing the Volume Up/Down buttons on your device will no longer change the volume of your app since you’re overriding those keys too.
Since you’re app is only interested in the back key, I recommend that you only return true from within your “back” key if condition block and return false at the bottom of your function.
One more thing. I also recommend that you use the “down” phase for the “back” key. The reason is that some of the old Galaxy Tab tablets will not give you an “up” phase for the back key if you release the button after holding it down for about 2 seconds. The reason they do this is because they use that button (in combination of another button) to take screenshots after holding it down for that long. Just one of those Android gotchas. 
Thanks Joshua
i have implemented your recommendations and it worked perfectly … i appreciate your time and advice … perfect corona support.
Regards
Abdul