Developing pages for mobile devices is a very different challenge than developing pages for standard Web browsers. One of the biggest differences is the available screen space. A typical mobile device (such as a cell phone) can only display 15 characters across and four characters down. A typical desktop Web browser, in contrast, can display 80 characters across and 40 characters down.
Another challenge concerns bandwidth. Most mobile devices do not have blazing-fast connections to a network. When you use a mobile device, you typically get to enjoy watching each character slowly walk across the network and be displayed on your screen. Therefore, sending pages full of rich graphics and sound effects simply won't work.
In response to the unique characteristics of mobile devices, several alternatives to HTML were developed that are tailored specifically for mobile devices. These alternatives include HDML, WML, cHTML, and XHTML. The primary challenge of creating pages that are compatible with mobile devices is the challenge of creating pages that will render content that is compatible with all these different standards. The ASP.NET Mobile Controls do precisely that.