display_only_postal_code_on_billing_field.php

<?php
/*
	Hide billing address fields and make them optional.
*/
//css to hide the fields
function wp_head_hide_billing_fields()
{
	global $post, $pmpro_pages;
	if(empty($pmpro_pages) || (!is_page($pmpro_pages['checkout']) && !is_page($pmpro_pages['billing'])))
		return;
?>
<style>
	#pmpro_billing_address_fields .pmpro_checkout-fields div {
	    display: none;
	}
	#pmpro_billing_address_fields div.pmpro_checkout-field.pmpro_checkout-field-bzipcode {
    display: block;
	}
</style>
<?php
}
add_action('wp_head', 'wp_head_hide_billing_fields');
//make sure they aren't required
function my_pmpro_required_billing_fields($fields)
{
	if(is_array($fields))
	{
		unset($fields['bfirstname']);
		unset($fields['blastname']);
		unset($fields['baddress1']);
		unset($fields['baddress2']);
		unset($fields['bcity']);
		unset($fields['bstate']);
		unset($fields['bcountry']);
		unset($fields['bphone']);
	}
	return $fields;
}
add_action('pmpro_required_billing_fields', 'my_pmpro_required_billing_fields');