WooCommerce Checkout - only require email address

<?php
/*
Plugin Name: WooCommerce - Minimal Required Fields
Plugin URI: http://www.damiencarbery.com
Description: Experiment with the minimal number of fields required to complete PayPal payment.
Author: Damien Carbery
Version: 0.1

$Id: $
*/


// See: http://docs.woothemes.com/document/tutorial-customising-checkout-fields-using-actions-and-filters/
add_filter( 'woocommerce_checkout_fields' , 'wmrf_remove_checkout_fields' );

// Our hooked in function - $fields is passed via the filter!
function wmrf_remove_checkout_fields( $fields ) {
    // Remove all billing fields except the email field.
    unset($fields['billing']['billing_first_name']);
    unset($fields['billing']['billing_last_name']);
    unset($fields['billing']['billing_company']);
    unset($fields['billing']['billing_address_1']);
    unset($fields['billing']['billing_address_2']);
    unset($fields['billing']['billing_city']);
    unset($fields['billing']['billing_postcode']);
    unset($fields['billing']['billing_country']);
    unset($fields['billing']['billing_state']);
    unset($fields['billing']['billing_phone']);

    unset($fields['order']['order_comments']);

    return $fields;
}