sms-pager/app/views/pages/page.html.haml

= form_for :page, url: send_page_path do |f|
  = f.label :person_id
  = f.select :person_id, options_from_collection_for_select(@people, :id, :name, @page.person_id), include_blank: true

  = f.label :to
  = f.phone_field :to

  = f.label :message
  = f.text_area :message

  = f.submit 'Send Page'

:javascript
  var people = #{@people.to_json};
  $('#page_person_id').on('change', function(){
    $('#page_to').val( getPersonPhone($(this).val(), people) );
  });