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Amid the throngs of humanoid robots, car concepts and futuristic displays at Mobile World Congress in Barcelona, dozens of people swarm around one particular stand. From a distance, it appears to be one of many booths showcasing yet another smartphone lineup. But a closer look reveals what everyone's eagerly trying to get their hands on: a remarkably slim phone unlike anything I've ever seen.On display is Tecno's Spark Slim phone concept, a handset measuring 5.75mm thick (skinnier than a standard pencil) and weighing only 146 grams, according to the company. After waiting about 15 minutes for my turn, I pick up the coveted phone and am instantly amazed. It's light as a feather and yet doesn't feel like something I can snap in half. I do my own visual thickness test by pulling a pen out of my backpack and comparing it: the Spark Slim is, in fact, notably thinner.Tecno isn't the only company that seems to believe slim is in. A few halls down, Samsung displays its Galaxy S25 Edge, which remains just out of reach behind a barricade, surrounded by a similarly impenetrable crowd of eager spectators. Details on that phone, from specs to release date, are just as slim as its appearance. But reports suggest we'll see it sometime this year.Read more: Best of MWC 2025: Affordable Phones and Cool Camera ConceptsOppo, too, has launched the Find N5, which it calls the "world's thinnest book-style foldable," measuring just 8.93mm thick when closed and 4.21mm thick when opened. The size and shape blew me away when I tested it, and helped assuage some of my reservations about the practicality and bulkiness of other foldables. And perhaps one of the biggest rumors leading up to the anticipated release of the iPhone 17 lineup is a potential iPhone "Air," a thinner (and presumably lighter) version of Apple's handset. The Tecno Spark Slim phone concept is thinner than a pencil. It felt super light in my hand. Abrar Al-Heeti/CNETBut a thinner phone, while a cool flex, can lead to drawbacks. Less space often means a smaller battery, and therefore shorter battery life. Camera hardware can get scaled back, too, leading to lower image quality. Storage space can similarly take a hit. These are all major concessions for phone buyers, who still rank battery life, camera quality and storage space among their top priorities.Pushing the limits can be disastrous, as Samsung learned when it opted to slim down the design of the Galaxy Note 7, only fordevices to start smoking and for the phone to ultimately be recalled. Phone makers also have to keep durability at the forefront, especially if buyers are paying a pretty penny and expect their devices to last."You can't just be thin; you have to still have all the bells and whistles of a premium phone," Nabila Popal, senior director of data and analytics at IDC, tells me at MWC. "The question is, how are OEMs [phone makers] going to achieve that without compromising the other more important features like battery and camera?" The Galaxy S25 Edge is coming, we just don't know when -- or any other details. Abrar Al-Heeti/CNETThat'll be the challenge as more companies undoubtedly lean into the thin phones trend. But if it's not necessarily what consumers have asked for in droves, why bother slimming down devices?"For the most part, it's an attempt for OEMs to differentiate," Popal says. While generative AI was the clear spotlight-grabber during last year's MWC, it's become so ubiquitous that this year, the focus has been more about strategy and implementation. Therefore, phone makers need to find a new way to stand out, and an eye-catchingly slim and appealing light device is one way to do that. This approach seems to be working in places like China, where companies like Honor, Xiaomi and Huawei have all debuted slim premium devices (which often double as foldables, too). But Popal adds that just because something resonates in China doesn't necessarily mean it will in other parts of the world, as consumers in China tend to be more receptive to unique phones than they are in America. But it illustrates that, at least somewhere, slim phones are already striking a chord.Read more: MWC 2025: The Weirdest Phones We've Seen in Barcelona So FarApple releasing a thinner phone could be particularly advantageous, especially as it struggles to differentiate its iPhones from each other, says Anisha Bhatia, senior analyst of consumer platforms and devices at GlobalData."For example, the iPhone 15 Plus model currently occupies an uncertain position in Apple's lineup, wedged between the base model and the more feature-rich Pro and Pro Max versions, Bhatia says. "This ambiguity has led to confusion among consumers, who struggle to differentiate the Plus models based on value proposition and feature set. Sales data indicates that the Plus models have underperformed in comparison to other iPhone variants."On the other hand, something flashy like a thin iPhone is easier to distinguish, and could have a better shot at capturing the attention -- and dollars -- of shoppers. The Oppo Find N5 is an example of a thin phone the doubles as a foldable, measuring just 8.93mm thick when closed and 4.21mm thick when opened. Andrew Lanxon/CNETSo in a few year's time, will the very phones that MWC 2025 attendees eagerly crowded around be in their pockets and hands, now capturing photos of whatever is deemed the next tech innovation? Will thin phones become ubiquitous and win?"Thinness is not going to be a must-have, but it is definitely a feature that makes a phone feel more premium, and it's a nice to have," Popal says.What was once revolutionary often becomes the norm. Just a few years ago, a bigger phone screen was considered a special feature, but has now become standard. Alternatively, foldable phones have largely stayed niche, even more than five years after the debut of the Samsung Galaxy Fold. Slim phones could go down either route; it's just too early to predict, Popal says.Also, what's old is new again. The trend toward thinner phones harkens back to the popularity of Motorola's original Razr, which became a pop culture phenomenon upon its release in 2004 because of its slim build, unique shape and trendiness (who wouldn't want a hot pink phone just like Paris Hilton's??). Motorola's been working to recapture that zeitgeist by reviving the Razr phone line in the form of a foldable smartphone.Back to the present day, even if skinny phones don't end up going mainstream, that might not be such a bad thing, Popal suggests."I would argue, why do you want to make it the norm? Keep it niche, keep it premium," she says. "The sooner it becomes a norm, the sooner the profitability goes."And the sooner crowds move on to swarm around the next big (or slim) thing. Watch this: First Look at Samsung's Surprise Galaxy S25 Edge 01:53
