Up until now, the International Telecommunications Union has only considered LTE-Advanced and WiMAX 2 to be "true" 4G, but it looks like something has made the organization change its stance. During a meeting in Geneva on December 6th, the ITU said that the term 4G "may also be applied to the forerunners of these technologies, LTE and WiMax." The ITU also said that the 4G name could be used to describe "other evolved 3G technologies" that show considerable improvements compared to the original 3G in use.
It's not clear what exactly made the ITU change its mind on just what is and isn't 4G, but all that really matters is that they did. Now the carriers can feel free to advertise their networks as 4G without having to worry about facing the wrath of the UN agency (not that that stopped them before).