Custom url theme for drupal
If you are using Drupal6 Have a look at Mobile Tools module.


  The Mobile Tools module provides Drupal developers with some tools to
  assist in making adjustments to your site based on the visitor's
  device.


Once you install the module you can define different paths for desktop and mobile, then browser will detect the device and redirect to corresponding path.
For Drupal 7 Mobile Switch module is the alternative