It's been a while since we've seen an ASUS smartphone that wasn't meant to be used with (or as) a tablet, but the company is making up for that absence by launching the Zenfone line. The Zenfone 4, 5 and 6 all sport dual-core Intel Atom processors and a range of exotic color options. They also tout a new interface layer on top of Android 4.3, ZenUI, that promises both simplicity and a What's Next feature for tracking your daily schedule. Differences between models largely boil down to screen size and performance. The Zenfone 4 starts things off with its namesake 4-inch 800 x 480 LCD, a 1.2GHz Atom chip, a 5-megapixel rear camera and a front VGA shooter. Move to the Zenfone 5 and you'll get a larger 720p display with pen and glove support, a 2GHz Atom, an 8MP back camera and 2MP at the front. The Zenfone 6 builds on this with an even bigger (though still 720p) screen and a 13MP rear camera. ASUS hasn't said when the Zenfone series hits shops, although the absence of LTE suggests that the handsets won't reach 4G-obsessed US carriers in an official capacity. They'll definitely be cheap to buy off-contract, however -- the Zenfone 4 starts things off at $99, while its 5- and 6-inch counterparts will cost $149 and $199.