#config/initializers/mime_types.rb
Mime::Type.register_alias "text/html", :iphone

#Make a copy of app/views/layouts/application.html.erb calling it application.iphone.erb

#Make copies of the necessary view files in your controllers, calling them things like index.iphone.erb

#in Controller
respond_to :html, :iphone

#in ApplicationController
def self.responder
    MobileResponder
end

class MobileResponder < ActionController::Responder
  def to_format
    super
  rescue ActionView::MissingTemplate => e
    if request.format == "iphone"
      navigation_behavior(e)	    
    else
      raise unless resourceful?
      api_behavior(e)
    end
  end
end  

#in ApplicationController, set iphone format in before_filter。。。！！Maybe not need?
before_filter :check_format

def check_format 
    if request.env["HTTP_USER_AGENT"].downcase.match(/iphone/)
        request.format = "iphone"
    end
end