1. WPtouch Mobile Plugin
Best mobile plugin which help your site to run on mobile smoothly. WPtouch add simple & elegant mobile theme for mobile visitors of your WordPress site.
So if your theme is not mobile friendly then you can use this plugin and ensure to not drop your SEO ranking due to not having site on mobile platform.
It provide you fast, secure, user friendly & stylish platform for mobile visitor and keepexisting theme for desktop version.