Drupal isn't just a web-based content management system - you can use Drupal as the backend for mobile application development. Drupal can contain your content, business logic, user management, and search functionality, and your app can be a front end that talks to Drupal using the Services module.
The demand for mobile apps development is ever-increasing with the expanding community of Smartphone users. Mobile applications have taken the consumers and businesses by a storm. Several small, medium and large business enterprises have already attained huge ROI streaming the benefits of mobility solutions. Many more are planning to convert to mobile apps or build new apps. So question is can you use Drupal to build a mobile website. The answer is yes. Why not?
Once you have your drupal website setup, you can create, use or modify a pre-existing mobile theme. You can find a few on drupal.org . Bare minimum theme http://drupal.org/project/mobile
There are a few other themes you can try out. They're still in an early development stage, but it should be fine. Just make sure to subscribe to the development status feeds so you'll be informed when updates and patches are available.
Check out this page for more information on building Web apps using Drupal