Configuration/Core/client/html/common/address/billing/optional

Summary
List of billing address input fields that are optional

client/html/common/address/billing/optional = Array (   [0] => order.base.address.company    [1] => order.base.address.address2 )


 * Default: Array
 * Type: array - List of field keys
 * Since: 2014.03

Description
You can configure the list of billing address fields that customers can fill but don't have to before they can continue the checkout process. Available field keys are:
 * order.base.address.company
 * order.base.address.salutation
 * order.base.address.firstname
 * order.base.address.lastname
 * order.base.address.address1
 * order.base.address.address2
 * order.base.address.address3
 * order.base.address.postal
 * order.base.address.city
 * order.base.address.state
 * order.base.address.languageid
 * order.base.address.countryid
 * order.base.address.telephone
 * order.base.address.telefax
 * order.base.address.email
 * order.base.address.website