Mobile phone content vs Internet content
What I have found during my time in Japan, which I admit does have slightly differing phone usage culture patterns to the west, is that there is a distinct difference between the way mobile content and PC based content are used. This is something important to consider because, as you are aware Japan is a market leader in terms of number of accesses to content-based services on the mobile phone ( thanks to DoCoMo's i-mode ) and so might be taken as indicative as to how the market will progress in the west.
When delivering to the mobile phone content has to be trimmed down not only in terms of images and other decorative paraphernalia but also in terms of the length and depth of sentences used to convey its messages. Mobile sites are used, in the whole, for short term, quick-fix surfing whilst on the go, the other main usages are for downloading multimedia content to the phone ( mp3, ring tones and wallpapers ) and access to 'utility sites' such as timetables and directory services. Again the length and depth of these types of content has to be cut down from the normal output to a browser for the site to be a success on the mobile phone.
This is due to the natural, physical limitation imposed by the size of the screen, the keypad and the by the mobile, 'access from anywhere, anytime' usage philosophy of phone browsing - you do not want to be wading through reams of text when you are only on-line for two minutes whilst waiting for a train.
Other considerations such as image sizes, and by this I mean file size in KB, and pixel resolution of images have to be considered as well. It is no good providing the same rich content that you would display on your website for the current generation of phones available. Images still take time to download, time which mobile users are not prepared to wait for, and large, high resolution graphics, especially when containing text, become hard to read when rendered on the small screen.
My point is this : There is a definate need for seperate content for PC and Mobile sites and people should start considering these requirements when planning their mobile campaigns.