The C910 is a webcam, so no need for a steadycam and it's not really portable. The video is great and, if you don't want to mess with settings, you can turn on autofocus and autolight and the video will look perfect. Plus the stereo microphones really pick up a lot of audio without you having to yell or be close to it. I believe there's autosound as well.
The Kodak Playsport Zx3 is a great candidate for a steadycam mount, and it could probably use it. It takes pretty good video, but the microphone doesn't pick up audio as well. You can get this one really cheap, since there's a newer model out.
It depends on your reasons for getting the iphone...If it is speed you are after then version 5 may help but it will probably cost more. My Android operates at the 3g speed and is perfect for me...good luck and cheers.
My webcam is good, but not mobile. I need something a somewhat better than a webcam, but not within the price range of professional cameras. What has been suggested so far gives me a basis to work from and do some decent research.