The iPhone 4S is already a pretty decent camera. You can take pretty decent photos and videos with it. But there are accessories available for the device that would let you go about doing that more conveniently. Take the iPhone Shutter Grip. It is a pretty simple add-on that attaches to your phone and improves your grip. This makes your phone feel more like a regular camera.
This $40 grip connects to the charging slot and hugs your phone so you can hold it in a more secure fashion. It might even fit over your case. You get photo and video buttons with this, which could lead to less shaky photos. Switching from photo to video mode is pretty easy. What’s nice about this attachment is that it lets you capture steady photos more conveniently. It even has a tripod mount.
The iPhone Shutter Grip is exciting but it does not turn your phone into a DSLR. The Flash Dock for iPhone does not do that either. But it does let you attach your phone to your DSLR to capture high quality photos in a smarter fashion. It essentially marries your phone to your DSLR, so you can geo-tag your photos and share them more easily.
In order to share photos like a pro with this, you are going to need an Eye-Fi card. The transfer happens wirelessly. The Flash Dock also lets you use the built-in GPS in your phone to geotag your photos (using GPX files). This can be done over Bluetooth as well. The Flash Dock is available for $39.95 at the time of this writing.