Redirect mobile devices to alternate URL with Varnish 3.0 and Drupal 6

This is a short note for ourselves, but it might help others considering the (new for now) rules of Google indexing of non-mobile sites. Drupal 6 does not really provide all the stuff that would be really useful to switch the theme of your site depending on the browser being on a mobile device or not. There are a few modules that should help you, like switchtheme, and mobile_subdomain, but in the end, you can also do it as follows.

Setting up Apache (or web server x)

Let's assume your site is called and you want mobile devices to see another theme. Define the