What is 4G? It depends who you ask.
The ITU Radiocommunication Sector (ITU-R) defines 4G as International Mobile Telecommunications Advanced which is a cellular system that must have target peak data rates of up to approximately 100 Mbps for a high mobility connection and 1 Gbps for low mobility.
On the other hand, you have a carrier like Sprint which is marketing its WiMax network as “The first and only wireless 4G network from a national carrier”. Their WiMax network has a target peak of 10 Mbps, but real world tests place the speeds between 3-6 Mbps. It is still a heck of a lot faster than most 3G networks, so Sprint felt justified in calling it 4G.
So really, 4G is just a marketing term.
See the original post: T-Mobile to launch nationwide “4G” in 2010 – Android and Me