The iPhone 3G is not comparable to any phone on either Sprint or Verizon for the simple fact that the 3G data on AT&T's network is so very very limited in coverage area. So sure it can be faster, but when you can't use it in the vast majority of the country, what's the point?
http://forums.macrumors.com/showthread.php?t=482409
My 2 cents (and I am a VZW employee, indirect channel)
And here is a good article about WiMax and LTE----
http://wirelessrain.wordpress.com/20.../lte-vs-wimax/