gistfile1.nginxconf

server {  
  listen 80;
  server_name www.mysite.com;

  root /path/to/main_site;
  # ...

  location / {
    proxy_set_header X-Real-IP $remote_addr;
    # ...

    if ($http_user_agent ~* '(iPhone|iPod)') {
      set $iphone_request '1';
    }
    if ($http_cookie ~ 'iphone_mode=full') {
      set $iphone_request '';
    }
    if ($iphone_request = '1') {
      rewrite ^.+ http://m.mysite.com$uri;
    }

    # serve cached pages ...

    if (!-f $request_filename) {
      proxy_pass http://app_server;
      break;
    }
  }
}

gistfile2.nginxconf

upstream m_app_server {  
  server 0.0.0.0:3001;
}

server {  
  listen 80;
  server_name m.mysite.com;

  root /path/to/mobile_site;
  # ...

  location / {
    proxy_set_header X-Real-IP $remote_addr;
    # ...

    if ($http_user_agent ~* '(iPhone|iPod)') {
      set $iphone_request '1';
      set $iphone_path_prefix '/iphone';
    }
    if ($uri ~ ^/iphone.*$) {
      set $iphone_path_prefix '';
    }
    if ($uri ~ '(images|stylesheets|javascripts|\.css|\.js|\.ico|\.gif|\.jpg|\.png)') {
      set $iphone_path_prefix '';
    }
    if ($iphone_request = '1') {
      rewrite (.*) $iphone_path_prefix$1;
    }

    # serve cached pages ...

    if (!-f $request_filename) {
      proxy_pass http://m_app_server;
      break;
    }
  }
}

gistfile3.js

function createCookie(name, value, days, domain, path) {  
  var expires = '';
  if (days) {
    var d = new Date();
    d.setTime(d.getTime() + (days*24*60*60*1000));
    expires = '; expires=' + d.toGMTString();
  }
  domain = domain ? '; domain=' + domain : '';
  path = '; path=' + (path ? path : '/');
  document.cookie = name + '=' + value + expires + path + domain;
}

function readCookie(name) {  
  var n = name + '=';
  var cookies = document.cookie.split(';');
  for (var i = 0; i < cookies.length; i++) {
    var c = cookies[i].replace(/^\s+/, '');
    if (c.indexOf(n) == 0) {
      return c.substring(n.length);
    }
  }
  return null;
}

function eraseCookie(name, domain, path) {  
  setCookie(name, '', -1, domain, path);
}

gistfile4.html

<a href="http://www.mysite.com" onclick="createCookie('iphone_mode', 'full', (0.25/24), 'mysite.com')">  
  View full site
</a>