How to map user/password to a mobile theme?
You should be able to get around your problem (I say should because I haven't actually tried this):

Make a custom module that creates a menu item for the required url and makes it call the user password form.

/**
 * Implements hook_menu().
 */
function MODULENAME_menu() {
  $items = array();

  // A replica of the password reset page for mobile.
  // Based on the original menu item in user_menu().
  $items['m/user/password'] = array(
    'title' =&gt; 'Request new password',
    'page callback' =&gt; 'drupal_get_form',
    'page arguments' =&gt; array('user_pass'),
    'access callback' =&gt; TRUE,
    'type' =&gt; MENU_NORMAL_ITEM,
    'file' =&gt; 'user.pages.inc',
    'file path' =&gt; drupal_get_path('module', 'user'),
  );

  return $items;
}


I foresee you having to do this for some other pages too.

Personally I would probably not make a mobile site in this fashion, I would use the same pages for mobile and non-mobile and then make them look different based on screen size.