Here is a step by step, on how to set up AdSense for Mobile.
(1) Login to your AdSense account at google.com/adsense/.
(2) Click on AdSense Setup and you will see the AdSense for Mobile option at the bottom:
(3) Click on "Get Started" on the next page:
(4) Define your ads format, markup and colors on this page:
(5) Define a channel to track your mobile ads:
(6) Select your server side scripting language and copy and paste the code into your mobile pages: