Maxaud

This plugin allows you to define different CSS rules that get loaded into the page’s for specific devices.
Includes checks for 18 different tablet options and 13 different phone options.
This can be useful if you need to target specific phones or tablets to make CSS changes or show certain advertisements for certain devices.
For more options or if you feel like donating, check out the <a href="http://codecanyon.net/item/mobile-css-pro/3182318/" title="Mobile CSS Pro" rel="nofollow ugc">PRO version of Mobile CSS</a> that is available for purchase.

Mobile CSS

Allows you to define different CSS styles that get loaded for specific mobile devices.

Takayuki Miyauchi

This plugin allows you to switch theme according to the User Agent on the Nginx reverse proxy.
Nginx Mobile Theme’s requirements are as follows.
<ul>
<li>PHP 5.3 or later</li>
<li>WordPress 3.7 or later</li>
<li><a href="https://wordpress.org/plugins/nginx-champuru/" rel="ugc">Nginx Cache Controller</a> 2.0.0 or later</li>
</ul>
<h4>Some Features</h4>
<ul>
<li>You can flush mobile’s and pc’s each caches automatically via <a href="https://wordpress.org/plugins/nginx-champuru/" rel="ugc">Nginx Cache Controller</a>.</li>
<li>Allow you to switch theme according to the user-agent.</li>
<li>Allow you to customize multiple mobile device support via filter-hook.</li>
</ul>
<h4>Nginx Configuration</h4>
Add mobile device detection to the nginx.conf.
<pre><code>set $mobile '';
if ($http_user_agent ~* '(iPhone|iPod|incognito|webmate|Android|dream|CUPCAKE|froyo|BlackBerry|webOS|s8000|bada|IEMobile|Googlebot\-Mobile|AdsBot\-Google)') {
 set $mobile "@smartphone";
}
</code></pre>
Set proxy_cache_key.
<pre><code>proxy_cache_key "$mobile$scheme://$host$request_uri";
</code></pre>
Send custom request header to the backend.
<pre><code>proxy_set_header X-UA-Detect $mobile;
</code></pre>
Nginx Mobile Theme will switch theme when ‘@smartphone’ is received in the <code>$_SERVER['HTTP_X_UA_DETECT']</code>.
<h4>How to use</h4>
<ol>
<li>Please access to the theme-customizer in the WordPress admin area.</li>
<li>Please select Mobile Theme in the drop-down.</li>
<li>Click “Save & Publish” button to save.</li>
</ol>
<h4>Multiple mobile device support</h4>
<ol>
<li>Add custom mobile detection to the nginx.conf.</li>
<li>Add custom mobile detection to the WordPress via <code>nginxmobile_mobile_detects</code> filter-hook.</li>
</ol>
nginx.conf: 
 set $mobile ”; 
 if ($http_user_agent ~* ‘(iPhone|iPod)’) { 
 set $mobile “@smartphone”; 
 } 
 if ($http_user_agent ~* ‘iPad’) { 
 set $mobile “@tablet”; 
 }
In your custom plugin: 
 add_filter(‘nginxmobile_mobile_detects’, function(){ 
 return array(‘@smartphone’, ‘@tablet’); 
 });
<ul>
<li>As a result, allow you to select theme for @smartphone and @tablet individually in the theme-customizer.</li>
</ul>
<h4>Amimoto Support</h4>
The <a href="http://megumi-cloud.com/" rel="nofollow ugc">Amimoto</a> is a full-tuned WordPress AMI on the AWS EC2.
<ul>
<li>Uncomment /etc/nginx/conf.d/default.conf in line 17</li>
</ul>
before: 
 #include /etc/nginx/mobile-detect;
after: 
 include /etc/nginx/mobile-detect;
<ul>
<li>Add line to /etc/nginx/nginx.conf like following.</li>
</ul>
before: 
 proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; 
 proxy_set_header Accept-Encoding “”;
after: 
 proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; 
 proxy_set_header Accept-Encoding “”; 
 proxy_set_header X-UA-Detect $mobile; # add new line
<ul>
<li>
Define constant in the wp-config.php
define(‘IS_AMIMOTO’, true);
</li>
</ul>

Nginx Mobile Theme

This plugin allows you to switch theme according to the User Agent on the Nginx reverse proxy.

Mobile CSS vs Nginx Mobile Theme