Wherever crowds converge at Mobile World Congress, there's likely to be a thin or foldable phone -- or both -- on display. That was certainly the case at Tecno's booth, where the phone-maker showed off several concept devices with astoundingly slim designs. The Tecno Slim 2 is a follow-up to last year's Spark Slim, which I first saw as a concept at MWC 2025 before its eventual release. The upgraded model pares down the Spark Slim's 5.93mm frame even more, to 5.49mm. It's frankly a barely noticeable difference, given the minuscule unit of measurement. But it's a testament to how phone companies keep pushing the boundaries of mobile hardware to develop jaw-droppingly thin and light phones. The Slim 2 also has super-narrow 0.7mm bezels for more immersive viewing. The concept phone's settings lists some key specs, including a 6,150-mAh battery, which is especially impressive given its sleek build. The rear cameras are listed as 50 megapixels and 13 megapixels.…