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.

Robin Phillips

This plugin was originally written for a client, but may be useful for others. It simply creates a discrete banner when viewed on mobile. This banner can include a link, to a mailing list for example.

Mobile Banner

Create a banner with a link at the bottom of the screen, when viewed on mobile only.

Mobile CSS vs Mobile Banner