Problem with :touch in belongs_to

I've read in rails api that there is a touch parameter and I want to
use it in my application. I have something like that
class User < ActiveRecord::Base
  has_many :phones

  after_update :updated

  def updated
     ...
  end
end

class Phone < ActiveRecord::Base
  belongs_to :user, :touch => true
end

I want that every change of any phone number would change User
updated_at and also call user after_update callback.

But when I add :touch parameter I get error that looks like:

ArgumentError: Unknown key(s): touch
  from /Library/Ruby/Gems/1.8/gems/activesupport-2.3.2/lib/
active_support/core_ext/hash/keys.rb:47:in `assert_valid_keys'
  from /Library/Ruby/Gems/1.8/gems/activerecord-2.3.2/lib/active_record/
associations.rb:1506:in `create_belongs_to_reflection'
  from /Library/Ruby/Gems/1.8/gems/activerecord-2.3.2/lib/active_record/
associations.rb:994:in `belongs_to'
  from (eval):3:in `belongs_to'
  from /Users/arkadiuszmlynarczyk/TapConference/app/models/phone.rb:2

I've read in rails api that there is a touch parameter and I want to

It's not in rails 2.3.2.

Fred