code: public ListTemplateElementBuilder addPhoneNumberButton(String title,
  			String phoneNumber) {
  		Button button = ButtonFactory.createPhoneNumberButton(title,
  				phoneNumber);
  		this.element.addButton(button);
  		return this;
  	}
docs: Adds a button with a phone number to the current
  {@link ListTemplateElement}. There can be at most 3 buttons per element.
  
  @param title
  the button label.
  @param phoneNumber
  a phone number. Must be in the format '+' prefix followed by
  the country code, area code and local number.
  @return this builder.