jquery_useragent_sort.js

<script src="js/jquery_1.6.4.min.js" type="text/javascript"></script>
<script src="js/jquery.cookie.js" type="text/javascript"></script>
function detect_device() {
	var user_agent = [
		'iPhone',
		'iPad',
		'iPod',
		'Android'
	];

	var pattern = new RegExp(user_agent.join('|^'), 'i');
	return pattern.test(navigator.userAgent);
}

function smartphone_site() {
	var message = confirm("スマートフォンサイトを表示しますか？");
	if(message == true) {
		$.cookie('detect_device_mode', 'smartphone', {path: '/'});
		location.href = "./smartphone/";
	} else {
		$.cookie('detect_device_mode', 'pc', {path: '/'});
	}
}

if(detect_device() && $.cookie('detect_device_mode') == null) {
	smartphone_site();
} else if($.cookie('detect_device_mode') == 'smartphone'); {
	location.href = "./smartphone/";
}

<a onclick="smartphone_site" href="javascript:void(0)">change to smartphone_site</a>

useragent_hataccess.htaccess

#mod_rewite enabled on
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT}(iPhone|iPod)
RewriteCond %{QUERY_STRING} !mode=pc
RewriteRule ^$ /smartphone/ [R]
RewriteCond %{HTTP_USER_AGENT} iPad
RewriteCond %{QUERY_STRING} !mode=pc
RewriteRule ^$ /smartphone/ [R]
RewriteCond %{HTTP_USER_AGENT} Android
RewriteCond %{QUERY_STRING} !mode=pc
RewriteRule ^$ /smartphone/ [R]
RewriteCond %{QUERY_STRING} !mode=pc

useragent_sort.js

function detact_device() {
	var user_agent = [
		'iPhone',
		'iPad',
		'iPod',
		'Android'
	];

	var pattern = new RegExp(user_agent.join('|^'), 'i');
	return pattern.test(navigator.userAgent);
}

if(detect_device()) {
	location.href = "/smartphone/"
};