Being in the communications industry, I do not know how I allowed WiMAX, and LTE to slip by me unchallenged as 4G technologies. While they do have the ability, and will likely be upgraded to conform to the ITU standards of 4G, NO carrier currently has a 4G network. Not Clear. Not Sprint. Not Verizon. Not AT&T. And certainly not T-Mobile, who has been promoting "the largest 4G network".
T-Mobile has made upgrades to their GSM/HSPDA network, and have made a number of their towers HSPDA+. Upgrading to a HSPDA+ network, depending on the hardware installed on the network can be as simple as a software upgrade, and in no way constitutes the revolutionary changes that require an incremental change of the generation of the device or service.
HSPDA+ is more accurately a 3G+ technology, and FAR, FAR from being a 4G technology, regardless of how it stacks up to other so called 4G providers (as there are currently NO 4G carriers)
While AT&T and Verizon are going to be building out an LTE network, when they first come on line they will not truly be 4G, but are capable of obtaining 4G speeds within a year or so after they go on line. AT&T will have the advantage at building out their "4G" network, because LTE is the next evolution of GSM. Verizon however will have to build an entire network along side of their current network, and maintain 2 networks. They also will likely have to offer LTE/CDMA phones to prevent customers from reaching a dead zone while they build out their new network. (LTE is backwards compatible with GSM, so ATT will only need to maintain one network)
If HSPDA+ was a "4G" technology, then ATT would have upgraded to such a network already, but since it has no potential to ever become a 4G technology, ATT opted to bypass the upgrade to HSPDA+ and save their investment capital to build out their LTE network.
Now onto the Clear/Sprint WiMAX 4G claim. While the network does not currently obtain the speeds required to qualify for 4G, like LTE it is an entirely new network that carriers need to build out, which in my opinion should qualify it as 4G, or at least PRE-4G. Also it will be able to be upgraded to the speeds required to qualify as 4G within a year or so.