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Sorry, LTE compatibility in the U.S. still years away

The industry is working on making it so a 4G LTE phone on AT&T can work on Verizon Wireless, Sprint Nextel, or T-Mobile, but an answer won't come for a few years.

Apple's iPhone 5.
Unfortunately, AT&T's iPhone 5 is only LTE at AT&T. CNET

BARCELONA, Spain--Here's the good news: the U.S. wireless industry is working to ensure that you'll eventually be able to take your LTE-enabled phone from one carrier to another and get the same experience.

The bad news: it likely won't happen for a few years.

That's according to T-Mobile Chief Technology Officer Neville Ray, who spoke to CNET in an interview at Mobile World Congress. Ray says the industry is keen on phones that can operate on different carriers, but that there remain a lot of complexities.

The advent of 4G LTE technology was supposed to unify the industry, joining together factions that spent years in their respective technology camps, or CDMA and GSM. That's been a big hurdle, particularly in large countries such as the U.S. and China. In the U.S., for instance, phones can move between AT&T and T-Mobile USA, but will not work on Verizon Wireless or Sprint Nextel.

But alongside the rise of a common technology in LTE is a new problem: spectrum fragmentation. Because of the lack of consistent spectrum bands, carriers have built their networks using incompatible spectrum frequencies. AT&T and Verizon actually run on the same frequency, 700MHz, but are in different parts of the band and can't work with each other. T-Mobile and Sprint Nextel are each using their own different bands.

The industry is already doing a lot of work to address the complications. Qualcomm told CNET that it will solve the 4G LTE roaming problem this year by introducing a chipset that can run on multiple frequencies.

CNET broke the story that Verizon would have international roaming partners for its 4G LTE network by next year.

So while there's been progress on the chip side, there remains a problem with the radios and how many bands they can actually handle, Ray said. He added there were additional complications handling both low and high bands of frequency.

Another wrinkle: additional spectrum that will eventually be made available to the wireless industry that adds even more new frequencies. That comes on top of different bands of spectrum held by AT&T and Dish. So achieving interoperability is like hitting a moving target.

Verizon has said that while it may have some agreements in place next year, it will take some time for phones that are compatible with certain frequencies to hit the market.

Wireless carrier executives at the show were pushing for more "harmonization," or the use of similar bands of spectrum of LTE.

There seems to be more of a push for the carriers to work with international carriers than their domestic competitors. The carriers, of course, have a vested interest in keeping customerd locked into their networks, so the idea of interoperability may not be high on the list as a goal.

The legacy of network incompatibility, meanwhile, means these devices couldn't work together either way if a 4G LTE connection wasn't available.

Ray, who also serves as chairman of the 4G Americas trade group, said he is a big believer in consumer portability. Indeed, T-Mobile has pushed to get AT&T iPhones switched over to its carrier. But in many markets, those iPhones drop from a faster connection to a slower one because of spectrum incompatibility. Only in select markets do T-Mobile and AT&T have compatible bands for HSPA+, a fast network they both call 4G. But an iPhone 5 on AT&T wouldn't get LTE with T-Mobile.

How quickly this will get addressed depends a lot on how rapidly the industry puts the new bands of spectrum to use. Ray said he believes this is an important issue.

"Ultimately, that problem has to be fixed," he said.