function showEmailInput() {
  Element.hide('notification_for_sms');
  Element.hide('notification_for_iphone');    
  Element.show('notification_for_email');
  Element.show('subscription-time-options');
  Element.show('subscription-submit-button');
  $('tab_nav').className = 'tab_email';
}

function showiPhoneInput() {
  Element.hide('notification_for_email');
  Element.hide('notification_for_sms');
  Element.hide('subscription-time-options');
  Element.hide('subscription-submit-button');
  Element.show('notification_for_iphone');
  $('tab_nav').className = 'tab_iphone';
}

function showSMSInput() {
  Element.hide('notification_for_email');
  Element.hide('notification_for_iphone');    
  Element.show('notification_for_sms');
  Element.show('subscription-time-options');
  Element.show('subscription-submit-button');
  $('tab_nav').className = 'tab_sms';
}