def build(xml, start_index = 0)
    super do |xml|
      [:url, :name, :email, :position, :organization, :additional, :phone, :address].each do |key|
        if @vcard.has_key?(key)
          xml.tag!(key, @vcard[key])
        end
      end
    end
  end
def build(xml, start_index = 0)
    super do |xml|
      [:url, :name, :email, :position, :organization, :additional, :phone, :address].each do |key|
        if @vcard.has_key?(key)
          xml.tag!(key, @vcard[key])
        end
      end
    end
  end
allowed options:
   url
   name
   phone
     cell
     work
     fax
   email
   position
   organization
   address
      post_office_box
      street
      city
      region
      postal_code
      country
   additional