I'm a fan of using cold, not steamed, milk in an iced latte. I know there has been at least a few discussions on the use of cold vs. steamed vs. cold with scooped foam. If your gonna use espresso, I would say add it last over the milk (that way you dont risk melting a cold cup or getting a nasty plastic taste). Toddy concentrate as an espresso substitute in iced drinks is a pretty good way to go too. But yea, steamed milk or foam over ice can have a pretty nasty texture/taste, IMO. Hope that helps.
Syrup first (simple or flavored) if necessary. Cold milk to the halfway point. Fresh, hot espresso. Fill with ice. dump into a shaker and back to mix. Hot espresso will warp some cold cups, and will melt some of the ice if you add it on top, which is why we do it in this order.
A little steamed milk over ice to do an iced capp is pretty good... wouldn't do more than a few ounces though.