From the reviews of 4G ready phones in America it doesn't really seem like its worth it at the moment. It drains the battery much faster than WiFi and for the majority of usage 3G is more than enough.
The American 4G phones are based on WiMAX. European networks (and three of the four major US networks) are going to be using LTE.
LTE roll-out in this country is happening between now (!) and 2012. I'd expect to see it feature in broadband dongles before hitting phones. We might start seeing LTE phones in 2011 but it's not going to be mainstream for a while.