LTE connectivity is looking increasingly likely for Apple's new iPhone 5. Just hours ahead of Apple's widely rumored iPhone 5 event, sources have reportedly verified to The Guardian that 4G infrastructure vendors have been testing iPhone 5 LTE handsets compatible with EE's 1800MHz band 4G, and that Apple has apparently registered the new devices with the GSMA in filings yet to be made public.

LTE has long been anticipated for the new iPhone, particularly after the company included it in the new iPad, with Apple refusing to add it to the iPhone 4S over concerns about early radio chipset bulk and battery demands.

What's been more uncertain, however, is which exact bands the iPhone's LTE might be compatible with. Designing a mobile device that can handle the multiple LTE bands globally is quite a challenge. It's exactly why the "new iPad" is only compatible with AT&T and Verizon LTE networks in the US, and Bell, Rogers and Telus networks in Canada.

IDC analyst John Byrne estimated that there are 36 LTE bands globally. Meanwhile, he estimated that there are "only" 22 3G GSM bands around the world. No one iPhone could hope to cater to them all, meaning some countries (and operators) will be forced to do without 4G.

EE dropped a heavy hint at its launch Sept. 11 that a new device was fast incoming with LTE support for the UK network, though declined to confirm that it was, indeed, the iPhone. Previous leaks indicated Apple would attempt to spread compatibility among networks worldwide, though failed to specify which they might be.

According to this latest insider, UK iPhone 5 testing by Huawei, Nokia Siemens Networks, and Ericsson has been underway "for some weeks both in labs and in public places." In the US, the handset is expected to run on LTE networks operated by Verizon and AT&T, though we don't yet know whether a single device will deliver that or if Apple will release two versions.

While LTE is the future, it's still a burgeoning technology. The technology is much more fragmented than the previous third-generation wireless technology, making it more difficult to make LTE phones that work seamlessly around the world.

So far, only three countries have significant numbers of LTE customers: the United States, South Korea and Japan. According to IDC, Verizon currently has the largest LTE network in the world and the highest number of LTE subscribers, around nine million at the end of the first quarter.

With the iPhone 5 expected to sport 4G LTE tech, one analyst wonders whether Apple will have dealt with all of the "compromises" that CEO Tim Cook mentioned as an LTE deal-breaker last year.

It is "unlikely" that Apple will be able to deliver LTE without some compromises for its next iPhone, said Will Strauss, principal analyst at Forward Concepts, a market research firm that covers wireless communication chips, among other chip technologies.

4G LTE phones have been notorious for underwhelming battery life.

"First of all that chip is going to have to handle not only LTE but 3G and that means W-CDMA, CDMA, 1XEVDO, and things like HSPA+," said Strauss.

"And, frankly, Qualcomm is the only company on the planet that can provide such a chip, [but] power consumption is nothing to brag about. There's no free lunch. You get all that wonderful video and high-speed everything-you-could-want but there is a trade off," he added.

But, Strauss, like many of the rumors ciruclating about purported better battery life for the iPhone 5, believes Apple has likely made progress. "I'm sure there's been some improvement. And it's probably not just a matter of silicon improvement. Things such as power optimization, power management. That will make sure you're consuming power only when absolutely necessary," he said.

Cook addressed the iPhone and Verizon in April 2011 during the company's earnings conference call.

"I think you can see this in the products that have been shipped, is that the first generation of LTE chipsets force a lot of design compromises with the handset, and some of those, we are just not willing to make."

Certain models of Apple's Retina iPad come with 4G LTE, but that device is large enough to accommodate a relatively large battery. That won't be the case for an LTE iPhone.

Qualcomm offers chips that support LTE and various other standards that smartphone makers -- like Samsung and its Galaxy S III -- are essentially forced to use in the U.S. because of the idiosyncrasies of the U.S. market.

According to The Wall Street Journal, wireless carriers are eager to drive more customers to those networks, which are more efficient and could spur faster growth in data revenue by making it easier for consumers to use services like streaming video.

South Korea's SK Telecom is second with 2.75 million LTE subscribers, while Japan's NTT DoCoMo has 2.23 million, according to IDC.

Europe is still lagging in LTE adoption, with LTE service in Germany, Scandinavia, and elsewhere, but the technology is still in its infancy in most of Europe. Despite that, though, LTE is seen as a checkbox that Apple must meet to compete with its Android rivals, including Samsung.

LTE-capable Android phones are currently being sold in 11 countries including the U.S., Japan, South Korea, Australia and Germany, according to IDC.

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