If there's not an approved web app you're probably SOL. Unless you've jailbroken your phone you can't install anything natively.
The SDK comes out next month, which will let developers... well,
develop... applications for the platform. I don't have the slightest clue who's eligible for the SDK. I'm a 'developer' as far as signing up through Developer Connection, but I don't know if that guarantees access to the SDK. I doubt very much that Apple wants every Tom, Dick 'n Harry futzing up its hardware; the phone still needs to be secure.
But I'm just speculating. Surely someone here has some quality info!