From Aimee and Michael of Mobix Creative
There are few free, ‘only mobile’ themes for Drupal and I have selected the actively maintained ones. The others do not have Drupal 7 (dev or released) version or no recent updates…
Theme name: Mobile (Actively Maintained) (for Drupal 7 as well)
Mobile is designed as a mobile-only HTML5 theme with a focus on clean, readable, usable display of content and accessibility of functions. You can use the base theme, use one of the included child themes, or make your own child theme.
Theme name: Fusion Mobile (Actively Maintained)
(Drupal 7 version is in dev mode)
Fusion Mobile is a Fusion Core
subtheme designed for creating a custom theme targeting mobile devices. By using a separate subtheme, you can control your theme settings and block layout/contents specifically for mobile devices.
Theme name: jQuery Mobile (Actively Maintained)(for Drupal 7 as well)
The Mobile jQuery Theme is a powerful theme built on the jQuery Mobile
) platform. The theme adapts some of Drupal's base output to work with the highly themable designs built into the framework.
Great additional info:
(scroll down for good compatible plugins and extensions…
There are great responsive base themes as well (free):
Zen is a powerful, yet simple, HTML5 starting theme with a responsive, mobile-first grid design. If you are building your own standards-compliant theme, you will find it much easier to start with Zen than to start with Garland or Stark.
The Omega Drupal 7 Base Theme
is a highly configurable HTML5/960 grid base theme that is 100% configurable. Each zone (group of regions) can be configured for content first layouts (push/pull classes), hidden at any time and each region can be disabled, resized, and placed easily any way you see fit.
Adaptivetheme is a powerful theme framework designed from the ground up to power modern, cross browser/cross device websites using responsive design techniques. Adaptivetheme allows you to set up specific layouts for different device groups - such as desktop, tablet and smartphone - all with zero coding. Its all easy point-and-click configuration. The layout system is entirely pluggable, so while AT ships with many layout options by default you can easily extend this in your sub-theme with your own layout plugins.
There are several premium responsive theme out there (prices between $29-$100)