For what its worth, I've been doing a little more reading on this.
Saw another poster claim Sprint's 4G is really 3.5G....I think WiMax II may be true 4G. Supposedly, LTE is going to be a more widely adopted standard, and VZW is making plans to connect all your wireless stuff (like when all your electronics and appliances have WiFi). I don't fully understand the differences, but supposedly the spectrum VZW has rights to has better range and penetration than Sprints (which I'm sure VZW paid a premium for, and probably why we pay more for a better service), in addition to LTE being superior to WiMaxI
Again, I don't know if Sprint will be upgrading to the new standard, but average speeds of their 3.5G is supposed to be something like 2.5-5Mbps while VZW's tests of LTE users are reporting averages of 5-12Mbps. That's significant because it becomes a true broadband alternative capable of streaming HD tv and movies.
VZW wins again -
http://money.cnn.com/2010/02/23/technology/4g_networks/
"The No. 3 wireless carrier, Sprint Nextel (S, Fortune 500), claims to have a 4G network in place based on a different technology called WiMAX, though WiMAX is actually just an enhanced 3G technology. With more than 50 global carriers pledging to unveil LTE networks, some analysts have speculated that Sprint will likely commit to building its own LTE network in the near future."
The other interesting point in that article is to be considered 4G, it has to be capable of at least 100Mbps, but obviously they throttle down users so they have the bandwidth to avoid service issues. But I wonder if in the future, as more towers and pipes are put in place, if we don't eventually get 4G speeds of 25-50Mbps.
