Autofill billing Information on checkout page in Drupal Commerce
This code works for me.
function mymodule_form_alter(&amp;$form, &amp;$form_state, $form_id) { 
  global $user;

  if ($form_id == 'commerce_checkout_form_checkout' &amp;&amp; $user-&gt;uid) {
    $user = user_load($user-&gt;uid);
    $loaded_billing = commerce_customer_profile_load($user-&gt;field_commerce['und'][0]['profile_id']);
    
    // For each field in customer profile, fill the form field with the $user value.
    $form['customer_profile_billing']['commerce_customer_address']['und'][0]['#address'] = $loaded_billing-&gt;commerce_customer_address['und'][0];
    $form['customer_profile_billing']['field_telephone_number']['und'][0]['value']['#default_value'] = $loaded_billing-&gt;field_telephone_number['und'][0]['value'];
  } 
}

I tried to retrieve the commerce_customer_profile field list, but I didn't find a way to generalize an action for filling every field type in the form.