I've had the iPhone 4S since late October, and despite my previous reluctance in having such a device, I'm head over heels with it. Well, this might be an exaggeration because some of my friends and peers have really gone "extreme" with its photographic apps, and I'm not.
That said, I do like to use the various apps such as Instagram, Hipstamatic, Snapseed and the like that I have on mine. The lastest to appear is 646 Pro for iPhone whose claim sounds interesting. It claims that the app has been designed for professional and serious amateur photographers, and is the first and only iPhone camera app to give TIFF image files that have no in-app post-processing applied and no JPEG compression.
Its JPEGs are enhanced by 645 PRO's seven Film Modes, inspired by classic film stock as used by top photographers. It's still being considered for approval by Apple, but from the claims it makes, I'm sure many serious iPhone photographers will lap it up (subject to its meeting these claims and depending on a sensible price, of course).
As for multimedia photographers enamored with the iPhone, here's the iPhone Boom Mic, a small microphone that provides iPhone videos "professional" style sound. The microphone attaches to the iPhone's headphone jack. It's very lightweight, has a broad directional and a super-directional setting for more precisely focused recording.
Note: I have no direct or indirect relationship with either of these manufacturers and/or products.