@MunkiCloud checked out the DIY Point and Shoot video stabilizer I made for my Canon SX210 and modified it to mount the new iPhone 4. For a walking and panning shot, I think this DIY Stabilizer for that iPhone 4 came out great. Sometimes it takes a bit of 'dialing in' on how much weight to use and how far to spread those weights. Practicing if you've never used any type of stabilizer is also key. So before you drop down about $900 bucks for an iPhone Cinema Kit, you might have better video results with this DIY stabilizer for probably under $10 bucks...
You can find MunkiCloud's full write up here, and more information on my DIY Video Stabilizer for small Point and Shoots found in my article here.
Above: Adapter for iPhone on DIY Point and Shoot Stabilizer
Below: Images of my DIY Point and Shoot Stabilizer