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And devices built for one band of radio frequency won't work on a network that uses a different band. In other words a Verizon 4G LTE smartphone that operates on 700MHz spectrum in the U.S. will not operate on TeliaSonera's 4G LTE network in Sweden, which uses spectrum in the 1800MHz band. There are similar spectrum differences among countries when it comes to 2G and 3G networks. But what's different about the shift toward 4G is the shear number of radios that must be supported to offer roaming. When 2G and 3G spectrum was allocated, regulators in various regions of the world were able to work together to develop more comprehensive spectrum plans that necessitated fewer radios in devices.

But now spectrum in almost every part of the world is harder to come by, which means more radios must be supported in devices to allow for international roaming, Some experts in the industry say that the lack of cohesive spectrum planning has fragmented the market so much that it will be difficult and expensive for device makers and carriers to ever make roaming from one LTE mountain mysteries iphone case network to another anywhere in the world as seamless as it is today for mobile subscribers to roam onto 3G networks, "We'll likely see some LTE roaming between different regions and carriers," said Chris Pearson, president of the industry trade group 4G Americas, "But it won't be worldwide roaming."But others are more optimistic, Dan Warren, senior technology director for the GSMA, an international trade group promoting GSM technology throughout the world, is confident that technology advancements will prevail and save the day for future LTE device-toting globe trotters..

And he believes that technology is advancing rapidly to get more radio technologies handling more frequencies into devices at a much lower cost. "What's happening in terms of the number of radio technologies that can be added to a chip is not classic Moore's Law, but it's similar" he said. "There has been a lot of change in the past 9 to 12 months. And we're seeing chipsets go from single and dual frequency to four and five frequencies."Today's so-called "world" phones already need to operate in about six bands to get access to 2G and 3G networks around the world. To include LTE roaming, wireless devices will need another six or seven frequency bands, Warren estimates. This means that the next generation of truly mobile "world" devices will need at least 12 frequency bands.

Also, spectrum at higher frequencies is not ideal for indoor coverage, The reason is that signals at higher frequencies don't propagate as easily through obstacles, such as walls, This makes high-frequency spectrum problematic for in-building coverage, Spectrum in the lower bands is scarce mountain mysteries iphone case because it's already been allocated for other purposes, For instance, the 700MHz that U.S, operators are using for LTE was initially allocated for analog TV, The FCC was able to free up spectrum in this band when it forced TV broadcasters to broadcast in digital rather than analog back in 2009, This made more efficient use of spectrum and allowed the FCC to clear a large chunk of spectrum, which it auctioned off in 2007..

"The unemployment extension bill that recently passed in the U.S. and was signed by President Obama had some very positive elements in for freeing up unused TV broadcast spectrum," Pearson said. "But we were disappointed that that there was nothing about auctions for the 1755MHz spectrum."Pearson went on to say, "This spectrum would nicely pair with the already cleared 2150MHz AWS spectrum. In fact there are already 80 devices ready to take advantage of this spectrum combination. And Latin America was ready to follow as well."3G to the rescueThe good news is that regulators, engineers and wireless operators have some time to figure out some things. For now, there are few LTE networks for current LTE subscribers to even use when they travel. According to market research firm Wireless Intelligence, there are 52 live 4G LTE networks deployed in 30 countries. By contrast, there are 400 3G networks using HSPA.