rendering different html for mobile devices

Sorry if this is a bit OT - but I know people here like to help out!
Be grateful for any advice.

I'd like to render an html page but two versions.

- One version for mobile devices (iphones and blackberries specifically)
- One version for everything else

You can create 'fake' mime types for this. In a before filter you can
then set the format of the request based on the user agent. Then
instead of just having a foo.html.erb you have a foo.smartphone.erb
and foo.dumbphone.erb.

Fred