Originally Posted by ascii
It may be true that bandwidth is the correct term, but in the common vernacular most people just say "speed." You are wrong to bring up that distinction in the context of this conversation, which has not (up until this point) been highly technical.
But it's important distinction when talking about potential reasons why a tech isn't being incorporated. For one to say that LTE is fast enough is like one saying that if your car has a top speed of 200 MPH that you should be able to drive 1000 miles from one city to another in 5 hours. Speed isn't the sole factor to consider.
My background is computer network engineering. I've spent a lot of time on VoIP when it first started becoming popular. Consider that I can control the number of devices per network, that all connections are wired, and that all network speeds to each node is a constant yet even that had many issues because with VoIP you need it to be "real time" so those packets take a priority over everything else so the conversations don't have awkward pauses and there is no jitter.
Once you get that taken care of you need to make sure the rest of the network isn't bogged down by these priority packets. If that happens then packets get dropped, requests time out, etc. It's not good and unfortunately priority requests don't scale well. Note that FaceTime will never have the highest priority on a GSM/UMTS network. That will go to their voice calls first and foremost.
Remember, this is just VoIP, not VVoIP, so instead of just being voice it's voice and voice which is an entirely new level I've personally never dealt with on an enterprise scale. They have the wireless network speed. I think they probably have the backend bandwidth and necessary equipment to handle the load after 18 months sine its introduction for 100+ million devices that could potentially all FaceTime family and friends in a weekend to test it out (see Siri's debut with a couple million iPhone 4Ses) or during a holiday. These things need to be considered the same way you don't rebuild a highway based on off peak driving times. Again, all that's beside the point because it makes no sense to offer this with the new iPad when it seems ideal for iOS 6.