What do you think it takes to surf the web? The above image alone is 57KB.
This is no biggie unless you live in a country with ******** than **** network.
There is no reason why FaceTime couldn't be operational over 3G in most of Europe.
Keep in mind, Europe got iPhone MMS and tethering much earlier than people in the US using AT&T. With that trend, it'll be the same with Europeans getting official 3G facetime earlier than Americans.