Hi joel. That's nice trick. But i recommend to use this PHP mobile detection, as it can be used to detect any mobile platform, like Windows Mobile, Blackberry, Opera Mini, Android, Iphone, etc.

Found it here, and official site here

If you're looking to redirect users that visit your site on a mobile platform then you can embed this within your html file. It's a very simple JavaSript code.

<script type="text/javascript">
<!--
if (screen.width <= 699) {
document.location = "mobilevs.php";
}
//-->
</script>

All you have to do is simple replace the mobilevs.php with the location of your sites mobile version.