Why "oh-just-switch-the-css" dont work for creating mobile sites

   Well why not? With proper use of CSS, the page source itself is just the text content sans formatting so should be good for the little browsers right? Not exactly and here's why..

1. The needs of a mobile site user are *different* from that of a web user - nobody wants to see the same info they see on a regular web page on their mobile devices. Rather than trying to replicate what is on the web, mobile sites should try and address the needs that are specific to a mobile user - access to specific pieces of info, ability to easily navigate and perform critical actions etc. For example, the mobile site of web mail application would allow registered users to check their mails, Vs allowing new users to register via mobile site.

2. Website content is usually designed for the regular web page size (1024X768) which when displayed on mobile devices - whether PDAs (~320X~240), BlackBerrys (~240X~260), media phones (~220X~180) and other regular phones (~100X~100) - either gets mangled or looses visibility and context and may require considerable scrolling - both horizontal and vertical - to be visible. Another usability consideration is the user input - anything that needs typing should either be replaced or complemented with other alternatives.

3. Mobile devices are extremely resource constrained. Everything including CPU, power, memory and bandwidth (unless you have one of those all-you-can-eat plans) are usually at a premium. So by flooding the mobile device with regular page content, you are not only wasting costly mobile bandwidth, but there is a pretty good chance that you might be overloading the device resulting in unexpected behaviour (freeze? hang?), thereby permanently loosing a "mobile site" user, to say the least.

4. Mobile web technical standards are different from regular web. In fact there are multiple standards in the mobile world and depending on the carrier network and device/browser combination it varies from WAP and WML to HTTP and XHTML-MP with a number of others in between. However one thing that is common across these various standards is that none of them are HTML compliant - which means the chances of your regular web page, or even a reduced version of the same for that matter, getting displayed properly on a mobile device is slim to none. Not to mention the mobile specific issues like the WAP gap (for secure sites) and the latest .mobi TLD restrictions and standards that need to be addressed before the site is launched. Another major factor is the device variations - for example the cookie and Java script support is not uniform across all devices - so if your web site depends heavily on cookies or is AJAX based, or Flash for that matter, your site cannot be mobile "enabled" for sure. And last but not the least.. no popups on my mobile phone please ;)

   A full list of Mobile site issues, guidelines and best practices can be found at the W3C site