No. You do not need a mobile version of your website.
Creating a mobile version of your website is like creating a website that is a digital version of your brochure. It's amazing to speak with business professionals and have them ask (multiple times every day) about whether or not they should have a mobile version of their website. The reason you do not need a mobile version of your website is because mobile is not the same as the Web. From platform to technology to how the consumer interacts with the media, the only thing that that the Web and mobile have in common is that they are both (still) new media.
Mobile is not a smaller version of a website.
Mobile must be treated as a beast unto itself. ...
Mobile is something completely different. It's portable. Voice still plays a factor in it. It will not be manipulated by a keyboard or a mouse (it will be touch). The content and context must be easy to use, deliver results fast and give immediate value to the consumer. On top of that, mobile will (quickly) become the default platform of connectivity. So, once again, you do not need a mobile version of your website... you need to be thinking about your connected consumer and how you are providing them with the information, resources and content when they want it, where they want it and how they want it.
Interesting posting by Mitch Joel, but I do not agree. The mobile version of your website is a must. First you must make your website readable and consumable on mobile devices. And this is not a trivial job, but can be supported by tools like the Mobile Portal Accelerator. And then you need to think to take advantage of the unique capabilities of mobile devices.