I have my nginx conf file so that when ever a mobile device visits my site the url gets rewritten to m.mysite.com I did it by adding the following

set $mobile_rewrite do_not_perform;

if ($http_user_agent ~* "android.+mobile|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od)|iris|kindle|lge |maemo|midp|mmp|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|symbian|treo|up\.(browser|link)|vodafone|wap|windows (ce|phone)|xda|xiino") {
  set $mobile_rewrite perform;
}

if ($http_user_agent ~* "^(1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|e\-|e\/|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(di|rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|xda(\-|2|g)|yas\-|your|zeto|zte\-)") {
  set $mobile_rewrite perform;
}

if ($mobile_rewrite = perform) {
  rewrite ^ http://m.mywebsite.com redirect;
  break;
}

I got it from http://detectmobilebrowsers.com/ IT WORKS.But none of my images/js/css files load only the HTML. And I know its the chunk of code I mentioned above because when I remove it and visit m.mywebsite.com from my mobile device everything loads up.So this bit of code does SOMETHING to my css/img/js MIME TYPES. I found this out through the the console error messages from safari with the user agent set to iphone.

text.cssResource interpreted as stylesheet but transferred with MIME type text/html.
960_16_col.cssResource interpreted as stylesheet but transferred with MIME type text/html.
design.cssResource interpreted as stylesheet but transferred with MIME type text/html.
navigation_menu.cssResource interpreted as stylesheet but transferred with MIME type text/html.
reset.cssResource interpreted as stylesheet but transferred with MIME type text/html.
slide_down_panel.cssResource interpreted as stylesheet but transferred with MIME type text/html.
myrealtorpage_view.cssResource interpreted as stylesheet but transferred with MIME type text/html.
head.jsResource interpreted as script but transferred with MIME type text/html.
head.js:1SyntaxError: Parse error
isaac:208ReferenceError: Can't find variable: head
mrp_home_icon.pngResource interpreted as image but transferred with MIME type text/html.
M_1_L_289_I_499_default_thumb.jpgResource interpreted as image but transferred with MIME type text/html.
M_1_L_290_I_500_default_thumb.jpgResource interpreted as image but transferred with MIME type text/html.
M_1_default.jpgResource interpreted as image but transferred with MIME type text/html.
default_listing_image.pngResource interpreted as image but transferred with MIME type text/html.

here is my whole nginx conf file just incase...

worker_processes  1;

events 
{
    worker_connections  1024;
}


http 
{
    include       mime.types;
    include       /etc/nginx/conf/fastcgi.conf;
    default_type  application/octet-stream;
    sendfile        on;
    keepalive_timeout  65;

    #server1
    server {

        listen       80;
        server_name  mywebsite.com www.mywebsite.com ;

        index  index.html index.htm index.php;
        root   /srv/http/mywebsite.com/public;

        access_log /srv/http/mywebsite.com/logs/access.log;
        error_log /srv/http/mywebsite.com/logs/error.log; 


        #---------------- For CodeIgniter ----------------#
        # canonicalize codeigniter url end points
        # if your default controller is something other than "welcome" you should change the following
        if ($request_uri ~* ^(/main(/index)?|/index(.php)?)/?$)
        {
          rewrite ^(.*)$ / permanent;
        }

        # removes trailing "index" from all controllers
        if ($request_uri ~* index/?$)
        {
            rewrite ^/(.*)/index/?$ /$1 permanent;
        }


        # removes trailing slashes (prevents SEO duplicate content issues)
        if (!-d $request_filename)
        {
            rewrite ^/(.+)/$ /$1 permanent;
        }


         # unless the request is for a valid file (image, js, css, etc.), send to bootstrap
         if (!-e $request_filename)
        {
             rewrite ^/(.*)$ /index.php?/$1 last;
             break;
        }
        #---------------------------------------------------#

        #--------------- For Mobile Devices ----------------#
        set $mobile_rewrite do_not_perform;

        if ($http_user_agent ~* "android.+mobile|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od)|iris|kindle|lge |maemo|midp|mmp|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|symbian|treo|up\.(browser|link)|vodafone|wap|windows (ce|phone)|xda|xiino") {
        set $mobile_rewrite perform;
        }

        if ($http_user_agent ~* "^(1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|e\-|e\/|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(di|rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|xda(\-|2|g)|yas\-|your|zeto|zte\-)") {
         set $mobile_rewrite perform;
        }

        if ($mobile_rewrite = perform) {
         rewrite ^ http://m.mywebsite.com redirect;
         #rewrite ^(.*)$ $scheme://mywebsite.com/mobile/$1;
         #return 301 http://m.mywebsite.com;
        #break;
        }
        #---------------------------------------------------#
        location / 
        {
            index  index.html index.htm index.php;
        }

        error_page   500 502 503 504  /50x.html;
        location = /50x.html 
        {
            root   html;
        }


        location ~ \.php$ 
        {
            try_files $uri =404;
            fastcgi_pass  127.0.0.1:9000;
            fastcgi_index index.php;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
            fastcgi_param PATH_INFO $fastcgi_script_name;
            include /etc/nginx/conf/fastcgi_params;
        }







    }#sever1

    #server 2
    server {

        listen       80;
        server_name  m.mywebsite.com;

        index  index.html index.htm index.php;
        root   /srv/http/mywebsite.com/public;

        access_log /srv/http/mywebsite.com/logs/access.log;
        error_log /srv/http/mywebsite.com/logs/error.log; 


        #---------------- For CodeIgniter ----------------#
        # canonicalize codeigniter url end points
        # if your default controller is something other than "welcome" you should change the following
        if ($request_uri ~* ^(/main(/index)?|/index(.php)?)/?$)
        {
          rewrite ^(.*)$ / permanent;
        }

        # removes trailing "index" from all controllers
        if ($request_uri ~* index/?$)
        {
            rewrite ^/(.*)/index/?$ /$1 permanent;
        }


        # removes trailing slashes (prevents SEO duplicate content issues)
        if (!-d $request_filename)
        {
            rewrite ^/(.+)/$ /$1 permanent;
        }


         # unless the request is for a valid file (image, js, css, etc.), send to bootstrap
         if (!-e $request_filename)
        {
             rewrite ^/(.*)$ /index.php?/$1 last;
             break;
        }
        #---------------------------------------------------#

        location / 
        {
            index  index.html index.htm index.php;
        }

        error_page   500 502 503 504  /50x.html;
        location = /50x.html 
        {
            root   html;
        }


        location ~ \.php$ 
        {
            try_files $uri =404;
            fastcgi_pass  127.0.0.1:9000;
            fastcgi_index index.php;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
            fastcgi_param PATH_INFO $fastcgi_script_name;
            include /etc/nginx/conf/fastcgi_params;
        }







    }#sever2

    }#http

I could just detect the mobile browsers with php or javascript but i need to make the detection at the server level so that i can use the 'm' in m.mywebsite.com as a flag in my controllers (codeigniter) to serve up the right view. I hope someone can help me! Thank you!