You could implement a UserControl and put it in your layout.master file.

In the usercontrol you could detect the user agent string of the browser and check the current url and if it is a mobile device and the url isn't your mobile url then redirect to your mobile url.

However, that said I think its not a good idea to redirect mobile users, as mentioned in the product information for my Mobile Kit Pro add on. If a user searches google and google shows a link to the page in your site that has content matching their search, then you redirect them to a page that does not have what they came for its a bad user experience. If your mobile site has the same information and you can redirect them to a page that has the same information/content as the one they searched for that would be ok, but that would require some really complex logic to know exactly which page they requested and which mobile page to redirect them to.

Hope that helps,

Joe