virtual_attributes_example.rb

class Person < ActiveRecord::Base  
  
  attr_accessor :cell_area_code, :cell_number
  
  before_save :merge_cellphone
  
  private
    
    def merge_cellphone
      self.cellphone = "(#{cell_area_code}) #{cell_number}"
    end
end

## in the view

<% form.inputs do %>
	<%= form.input :name, :label => "Nome" %>
	<li id="person_cell_number_input">
		<label for="person_cell_number">Celular<abbr title="Obrigatório">*</abbr></label>
		<%= form.text_field :cell_area_code, :size => 5 %> <%= form.text_field :cell_number, :size => 15 %>
	</li>
<% end %>