We all know video call has been around for years. I'm myself have been using it for 2 years. However, there are several limitation to video call technology:
1. It strictly requires 3G reception or higher, no less, so the area you are in is utmost important
2. It requires phone with front-facing camera, ideally (because some phone with only rear camera do have video call function)
3. It requires persons on both end of the video call to abide no 1 & 2
4. Data charges
5. Extreme lagginess of video frame rate
Thus, I don't see an evolution or even revolution is in the making.
Plus, now with iPhone 4, it has add in another two more limitations:
1. With iPhone 4, you can make a video call to another iPhone 4 only. not even 3Gs will get the special treatment, though without front facing camera, we know FaceTime is able to use the rear camera.
2. Wifi only for the time being.
I believe I understand the reason for using wifi for FaceTime. 3G/3.5G unable to give you the kind of user experience that you expect to get from video call. Low frame rate means both of your voice and video will response to the other caller after 3-4 seconds later. Being Apple, they wish to give the ultimate experience to their customer. And lousy frame rate is not what they have in mind. Since 3.5G is the fastest and widely use right now, they have to resort to wifi until LTE comes alive probably next year in the US. If LTE do start operational next year in US, probably we can expect iPhone 4G to be launched. And that will be the right tonic to FaceTime
long agi i always play 3g video call from my nokia phone with other friends and there is no data charges like u said