PCMag reports that Verizon and AT&T's upcoming LTE ("4G") networks will be incompatible with each other:
Thinking of unlocking a Verizon Wireless LTE phone for use on AT&T's network, or vice versa? Think again. Verizon Wireless confirmed today that its LTE phones will not "be compatible on other LTE networks in the U.S." because "the phones will be on different frequencies," according to Verizon spokeswoman Brenda Raney.
LTE is the next generation data transfer technology beyond 3G and is frequently labeled 4G.
It turns out that AT&T and Verizon will be using different frequencies for their LTE implementations which will make it more difficult for manufacturers to support both networks. Of course, it's possible to support multiple networks in a single device, but it does require additional consideration in communication parts and antenna design.
Apple presently offers two separate iPhone models to support Verizon's CDMA and AT&T's GSM networks, but Apple is expected to consolidate support into a single device with the iPhone 5. Meanwhile, rumors point to Apple holding off on supporting LTE until at least the 2012 iPhone revision.
Top Rated Comments
Problem is that the carriers have no incentive to encourage this behavior. Devices that are specific to narrow blocks of frequency are good for no one but the greedy carriers.
Note that ATT also uses AWS band (1700/2100 MHz) for some of it's LTE deployment. But, the argument above still applies: world-mode phones have been around for awhile.
* Yes, this has been assumed for a while, the news is that it's confirmed
* The Chinese company you are thinking of is China Mobile. Note, they are pursuing TD-LTE, but it is not proprietary in any way, it's a companion standard to FD-LTE.