User Agent distinction

gistfile1.js

function is_mobile () {
    var useragents = [
        'iPhone',         // Apple iPhone
        'iPod',           // Apple iPod touch
        'Android',        // 1.5+ Android
        'dream',          // Pre 1.5 Android
        'CUPCAKE',        // 1.5+ Android
        'blackberry9500', // Storm
        'blackberry9530', // Storm
        'blackberry9520', // Storm v2
        'blackberry9550', // Storm v2
        'blackberry9800', // Torch
        'webOS',          // Palm Pre Experimental
        'incognito',      // Other iPhone browser
        'webmate'         // Other iPhone browser
    ];
    var pattern = new RegExp(useragents.join('|'), 'i');
    return pattern.test(navigator.userAgent);
}

if (is_mobile()) {
    var newurl = document.URL.replace(/\.com\//,".com/i/");

    // Write some code here.
    // If you want to let mobile user redirect to mobile site,
    // write following code.
    //
    // window.location.href = newurl;

}

Redirect to mobile site.

If you want to let user who uses mobile browser redirect to mobile site,
write above content and save as ua.js.
Then, write script tag on HTML head.

<script type="text/javascript" src="/path/to/ua.js"></script>

This code redirect *.com to *.com/i/.
It means
http://foobar.com/ will be http://foobar.com/i/, and
http://foobar.com/foo/entry.php will be http://foobar.com/i/foo/entry.php.