How could I let rails render wml by default with render/redirect_to method in the controller

Hi all,

I am using rails to create a wap site. I have using the following code
in the rails to make it work:

Mime::Type.register “text/vnd.wap.wml”, :wml

def index
… # some unrelated code
respond_to do |format|
format.wml # index.wml.erb

and I created the view as index.wml.erb

It works well when I visit the site, but if I using redirect_to or
render method in the controller instance method, the browser will tell
me template missing like show.html.erb, which means rails try to
render the view by .html.erb rather than the wml.

Is there any way I could let rails always trying to render .wml by