Why do I need an extra page/subdomain for mobile devices?
Todays websites are content-rich on scripts, images, Flash animations and video. All those elements use a lot of bandwidth, and most mobile Internet providers charged by the amount of used bandwidth.
This can be at rates of $1.99 per Megabyte and more.
Naturally we want to keep the files for mobile devices as low on bandwidth usage as possible, thus we need a special subdomain or subdirectory for our mobile website presence.
The recently released 4th generation, also known as Beyond 3G, aims to provide broadband wireless access with nominal data rates of 100 Mbit/s to fast moving devices, and 1 Gbit/s to stationary devices defined by the 4G systems, offering peak bit rates of 326.4 Mbit/s.
So, there will be changes in Future, but even if there will be faster downloads, still remains the problem with large images to be displayed on little handhelds.
For both reasons, media dimensions size and download size, it is a good idea to create 2 different appearances for the big computer screen and for the little mobile view.
A subdomain could be: m.yourdomain.com ---or--- mobile.yourdomain.com
A subdirectory could be: yourdomain.com/m ---or--- yourdomain.com/mobile
The subdomain requires all new and separated content, whereas the subdirectory can use the already existing content or just parts of it.