If you've used a Novatel Wireless MiFi 3G Hotspot for Wi-Fi connectivity on the go, you know that it's basically like having a Wi-Fi router that you can carry with you anywhere. That means that anything that works on Wi-Fi -- including FaceTime video calling -- works over the 3G internet connection provided by the MiFi.
Beginning next Friday anybody with an iPhone running iOS 4.3 will have that Personal Hotspot capability running on their devices. Of course, your carrier will need to enable that capability and you'll probably need to sign up for a special Personal Hotspot data plan, but the Personal Hotspot functionality is now going to be built into your iPhone.
This means that you could set up Personal Hotspot on one iPhone to create your zone of Wi-Fi connectivity, then others can connect their iPhones to your Personal Hotspot. When they do so, they're connecting via Wi-Fi and can make FaceTime connections.
How does FaceTime actually work over a 3G internet connection? Back when FaceTime was new, my fellow blogger Erica Sadun and I checked it out over my MiFi (running on the Sprint 3G network). We found that it actually worked quite well, up to a point. If you tried to move the camera much, the image quickly degraded and eventually the FaceTime connection failed. However, when we were simply talking to each other and not moving our phones around (i.e., keeping the background image still), FaceTime worked nicely.
Apple wants you to use a real Wi-Fi connection with FaceTime. That is, they want you to be using Wi-Fi with a broadband connection behind it, not a measly 3G wireless connection. On the other hand, isn't it cool to know that within a week, you and your friends can set up your own Wi-Fi hotspots for connecting your Macs, iPads, and iPhones over FaceTime?