Accessing content on a mobile device is more limiting then accessing content from a PC. Before you create web sites for a mobile devices it is important to clearly understand these limitations.
The most important issue to understand is the visitors experience.
Many web sites use big graphics that look great on a PC but take up so much of the mobile screen there is no room remaining for content.
Web sites also use a lot of "rich media". That is moving images that look great on a PC but are not supported on most mobile devices.
Mobile devices are typically used in a very distracted environment. Visitors may be on a bus, on a train, at the store, eating lunch, or at work.
The mobile device screen is very small. This limits what the visitor can see and can make it difficult to read a large amount of content, view graphics, or see moving graphics.