Show Custom Customer Fields in Checkout

I've succesfully managed to add custom fields to the customer. However I need these fields to show up in onepage checkout.

I've overridden Mage_Customer_Block_Widget_Name and created my own customer/widget/name.phtml, added the attributes in the sql/xxx_setup/installer-x.y.z.php (added them to adminhtml_customer, customer_account_edit, checkout_register and customer_account_create) and they work fine in the admin site, however they just wont work on the checkout form. The field shows up, ~~but it has the wrong value and no label~~.

I'm clueless why does it work in the customer registration form but doesn't in the checkout.

The installer code to add the attribute is:

$attributes = array(
    'lastname2' =>  array(
        'frontend_label'=>'Apellido Materno',
        'label' => 'Apellido Materno',
        'input' => 'text',
        'type'  => 'varchar',
        //System =  False and visible true = Show in 'customer_account_create', 'customer_account_edit', 'checkout_register'
        'system'=>true,
        'visible'=>true, //Watch out!! Only visible fields get processed by the form controllers!!!
        'user_defined'=>false,
        'used_in_forms' => array('adminhtml_customer', 'customer_account_edit', 'checkout_register','customer_account_create'),
        'required' => 0,
        'position' =>69
    ));


foreach($attributes as $attribute_code=>$definition)
    {
        $installer->addAttribute('customer', $attribute_code,  $definition); 

        /**
        * @var Mage_Eav_Model_Config
        */
        Mage::getSingleton('eav/config')
        ->getAttribute('customer', $attribute_code)
        ->setData('used_in_forms',$definition['used_in_forms'])
        ->save();
    }

The code in name.phtml is

<div class="<?php echo $this->getContainerClassName()?>">
    <?php if ($this->showPrefix()): ?>
        <div class="field name-prefix">
            <label for="<?php echo $this->getFieldId('prefix')?>"<?php if ($this->isPrefixRequired()) echo ' class="required"' ?>><?php if ($this->isPrefixRequired()) echo '<em>*</em>' ?><?php echo $this->getStoreLabel('prefix') ?></label>
            <div class="input-box">
                <?php if ($this->getPrefixOptions() === false): ?>
                    <input type="text" id="<?php echo $this->getFieldId('prefix')?>" name="<?php echo $this->getFieldName('prefix')?>" value="<?php echo $this->escapeHtml($this->getObject()->getPrefix()) ?>" title="<?php echo $this->getStoreLabel('prefix') ?>" class="input-text <?php echo $this->helper('customer/address')->getAttributeValidationClass('prefix') ?>" <?php echo $this->getFieldParams() ?> />
                    <?php else: ?>
                    <select id="<?php echo $this->getFieldId('prefix')?>" name="<?php echo $this->getFieldName('prefix')?>" title="<?php echo $this->getStoreLabel('prefix') ?>" class="<?php echo $this->helper('customer/address')->getAttributeValidationClass('prefix') ?>" <?php echo $this->getFieldParams() ?>>
                        <?php foreach ($this->getPrefixOptions() as $_option): ?>
                            <option value="<?php echo $_option?>"<?php if ($this->getObject()->getPrefix()==$_option):?> selected="selected"<?php endif; ?>><?php echo $this->__($_option)?></option>
                        <?php endforeach; ?>
                </select>
                <?php endif; ?>
            </div>
        </div>
        <?php endif; ?>
    <div class="field name-firstname">
        <label for="<?php echo $this->getFieldId('firstname')?>" class="required"><em>*</em><?php echo $this->getStoreLabel('firstname') ?></label>
        <div class="input-box">
            <input type="text" id="<?php echo $this->getFieldId('firstname')?>" name="<?php echo $this->getFieldName('firstname')?>" value="<?php echo $this->escapeHtml($this->getObject()->getFirstname()) ?>" title="<?php echo $this->getStoreLabel('firstname') ?>" maxlength="255" class="input-text <?php echo $this->helper('customer/address')->getAttributeValidationClass('firstname') ?>" <?php echo $this->getFieldParams() ?> />
        </div>
    </div>
    <?php if ($this->showMiddlename()): ?>
        <?php $isMiddlenameRequired = $this->isMiddlenameRequired(); ?>
        <div class="field name-middlename">
            <label for="<?php echo $this->getFieldId('middlename')?>"<?php echo $isMiddlenameRequired ? ' class="required"' : '' ?>><?php echo $isMiddlenameRequired ? '<em>*</em>' : '' ?><?php echo $this->getStoreLabel('middlename') ?></label>
            <div class="input-box">
                <input type="text" id="<?php echo $this->getFieldId('middlename')?>" name="<?php echo $this->getFieldName('middlename')?>" value="<?php echo $this->escapeHtml($this->getObject()->getMiddlename()) ?>" title="<?php echo $this->getStoreLabel('middlename') ?>" class="input-text <?php echo $this->helper('customer/address')->getAttributeValidationClass('middlename') ?>" <?php echo $this->getFieldParams() ?> />
            </div>
        </div>
        <?php endif; ?>
    <div class="field name-lastname">
        <label for="<?php echo $this->getFieldId('lastname')?>" class="required"><em>*</em><?php echo $this->getStoreLabel('lastname') ?></label>
        <div class="input-box">
            <input type="text" id="<?php echo $this->getFieldId('lastname')?>" name="<?php echo $this->getFieldName('lastname')?>" value="<?php echo $this->escapeHtml($this->getObject()->getLastname()) ?>" title="<?php echo $this->getStoreLabel('lastname') ?>" maxlength="255" class="input-text <?php echo $this->helper('customer/address')->getAttributeValidationClass('lastname') ?>" <?php echo $this->getFieldParams() ?> />
        </div>
    </div>

    <div class="field name-lastname">
        <label for="<?php echo $this->getFieldId('lastname2')?>"><?php echo $this->getStoreLabel('lastname2') ?></label>
        <div class="input-box">
            <input type="text" id="<?php echo $this->getFieldId('lastname2')?>" name="<?php echo $this->getFieldName('lastname2')?>" value="<?php echo $this->escapeHtml($this->getObject()->getLastname2()) ?>" title="<?php echo $this->getStoreLabel('lastname2') ?>" maxlength="255" class="input-text <?php echo $this->helper('customer/address')->getAttributeValidationClass('lastname2') ?>" <?php echo $this->getFieldParams() ?> />
        </div>
    </div>

    <?php if ($this->showSuffix()): ?>
        <div class="field name-suffix">
            <label for="<?php echo $this->getFieldId('suffix')?>"<?php if ($this->isSuffixRequired()) echo ' class="required"' ?>><?php if ($this->isSuffixRequired()) echo '<em>*</em>' ?><?php echo $this->getStoreLabel('suffix') ?></label>
            <div class="input-box">
                <?php if ($this->getSuffixOptions() === false): ?>
                    <input type="text" id="<?php echo $this->getFieldId('suffix')?>" name="<?php echo $this->getFieldName('suffix')?>" value="<?php echo $this->escapeHtml($this->getObject()->getSuffix()) ?>" title="<?php echo $this->getStoreLabel('suffix') ?>" class="input-text <?php echo $this->helper('customer/address')->getAttributeValidationClass('suffix') ?>" <?php echo $this->getFieldParams() ?> />
                    <?php else: ?>
                    <select id="<?php echo $this->getFieldId('suffix')?>" name="<?php echo $this->getFieldName('suffix')?>" title="<?php echo $this->getStoreLabel('suffix') ?>" class="<?php echo $this->helper('customer/address')->getAttributeValidationClass('suffix') ?>" <?php echo $this->getFieldParams() ?>>
                        <?php foreach ($this->getSuffixOptions() as $_option): ?>
                            <option value="<?php echo $_option?>"<?php if ($this->getObject()->getSuffix()==$_option):?> selected="selected"<?php endif; ?>><?php echo $this->__($_option)?></option>
                        <?php endforeach; ?>
                </select>
                <?php endif; ?>
            </div>
        </div>
        <?php endif; ?>
</div>

This fields in the checkout you are talking about are address attributes, not customer attributes. So you need to load them differently. For registered users you could use Mage::getSingleton('customer/session')->getCustomer()->getLastname2() but it won't be saved to your address, as there is no attribute yet.

Depending on where you want lastname2 to be accessible you can create corresponding attributes for the entities customer_address,quote_address and order_address. They are created the same way you did for customer with

$installer->addAttribute($entityName, $attribute_code,  $definition);

But that's not all. For the attributes to be converted correctly you need to set up conversion rules in your module config.xml. See for example the configuration of Mage_Sales. In the global node there is a node fieldsets with the corresponding rules. There is a node customer_address to convert address attributes to quote address attributes. In sales_convert_quote there are rules to convert this attributes to order attributes.

So for your attributes to be accessible in all you config should look like this:

<global>
   <fieldsets>
      <customer_address>
         <lastname2>
            <to_quote_address>*</to_quote_address>
         </lastname2>
      </customer_address>
      <sales_copy_order_billing_address>
         <lastname2>
            <to_order>*</to_order>
         </lastname2>
       <sales_copy_order_billing_address>
       <sales_copy_order_shipping_address>
         <lastname2>
            <to_order>*</to_order>
         </lastname2>
       </sales_copy_order_shipping_address>
       <sales_convert_quote_address>
           <lastname2>
              <to_order_address>*</to_order_address>
              <to_customer_address>*</to_customer_address>
           </lastname2>
       </sales_convert_quote_address>
       <sales_convert_order_address>
            <lastname2>
               <to_quote_address>*</to_quote_address>
            </lastnam2e>
       <sales_convert_order_address>
       <customer_address>
           <lastname2>
              <to_quote_address>*</to_quote_address>
           </lastname2>
       </customer_address>
   </fieldsets>
</global>