As the web continues to develop and evolve it is important to make sure your website has mobile capabilities. With Drupal this means one of three things for your web site:
Mobile Theme
For existing Drupal sites, the fastest, least expensive way to get started is to add a second theme to the web site that is designed for mobile devices. This approach detects what kind of device the user uses based on what the browser tells it, and if it detects a mobile device, redirects the user to a different location. Using a mobile theme, it's straightforward to create a separate mobile menu to highlight particular content, put that menu at the top of the page, and then the main content immediately below that.
Responsive Theme
A Responsive Theme is a great option that lets you make a single theme optimized for both mobile and larger screens. "Responsive" refers to their ability to change based on the browser size. Some themes move the sidebars of a site around to accommodate smaller screens, paying attention to tablet layout and switching between landscape and portrait. Others actually scale the width of their columns based on the width of the screen.
As of now, we are building all new Drupal 7 sites on top of responsive themes out of the box. All future sites will be mobile-friendly, at no extra charge.
Mobile Application
Building an App is all the rage these days. Everyone wants one, everyone believes their clients want one, but building an app for a smart phone and tablet is expensive and timing consuming. If you're writing an app that needs constantly fresh data, you need a data source online to feed to your app and get updates from your app. A Drupal site with Services module can be a powerful back end data source for mobile apps, with the added bonus of having a web browser front end out of the box! We've been doing web services for more than a decade, we can make an app-friendly interface to the powerful web storage engine that is Drupal.