The best method to redirect for mobile that I found is following:
<script type="text/javascript">
if (screen.width < 1081) {
var ref = document.referrer;
var urls = new Array("http://www.mymainsite.com","http://m.mymobilesite.com");
var n = ref.match(urls[0]);
var m = ref.match(urls[1]);
if ((m!==null) || (n!==null)) {
stop;
}
else if (ref=='') {
var r = confirm("Small Display is Detected.\nClick \"OK\" for MOBILE SITE.");
if (r==true) {
window.location = "http://m.mymobilesite.com";
}
else {
stop ;
}
}
else
{
window.location = "http://m.mymobilesite.com";
}
}
</script>