Well, not if the "new" device would be in another device class. In comparison with the notebooks - if Apple refreshed the Macbooks and shortly after introduced a new device called MacBook Pro, there would of course be some people complaining (they always do), but it would be something new and different, so the majority of customers might accept it.
Today a MacBook Pro line does already exist, but the iPhone is not yet diversified. So i could indeed imagine Apple introducing an iPhone Pro within a short timeframe in addition to the 3GS. The "pro" would be positioned higher and thus also priced higher (= revenue for Apple).
It worked great for Apple in the computer business: consumer device made of plastic, pro device with more/better features made of an optically different material - as metal on a phone might impair radio reception, that could well be something else, e.g. ceramic, carbon fibre or ... matte plastic!
Only question would be what is in the contracts with the exclusive distribution rights for selected phone providers in various countries - would a hypothetical iPhone Pro be covered by the contract (e.g. "all devices from Apple with phone capabilities for the next 5 years") or not? If not, they had no reason to complain and Apple could introduce something new and sell it independently from any phone provider...