Multiple inserts on a through association.

class Trunk < ActiveRecord::Base

  has_many :call_type_trunks
  has_many :call_types, :through => :call_type_trunks


class CallType < ActiveRecord::Base

  has_many :call_type_trunks
  has_many :trunks, :through => :call_type_trunks


class CallTypeTrunk < ActiveRecord::Base
  belongs_to :call_type
  belongs_to :trunk

The associaton class has a column named price. Each association
trunk/call_type will have a differente price.

When i choose to add a trunk. I want to list all call_types to allow
the users to add/edit both: the call_type ( associate or remove )
call_types to this trunk... and to edit price for each association
that exist.

How can I achieve this behavior?