Your TV is HD, your camcorder is HD, your games console is HD, even your pet cat is gloriously rendered in 1080 lines of progressively scanned video goodness -- so why not your mobile phone? At first thought, the idea of high definition in something small enough to fit in your hand seems ridiculous. Whatever next? HD digital watches?
But think again. We're living in an interconnected world, where digital content flows (fairly) smoothly back and forth across dozens of gadgets and screens. If just one of them can't handle HD video, it'll be about as popular as a Flash website at an Apple Store.
A fully featured HD phone needs to tick three boxes: it should be able to capture, display and output HD video. Displaying HD content is a good place to start, and that means a decent screen and a healthy processor. When it comes to watching high-def clips, the bigger the display, the better. A 3-inch screen should be the absolute minimum, 3.5 inches will be large enough to watch a full-length film and 4 inches (or even bigger) is the gold standard.
There isn't a phone out there with a genuine pixel-for-pixel high-definition screen. 800x480 pixels is typically the sharpest you'll find, although Apple's iPhone 4 famously boasts 960x640-pixel resolution. Also check out the technology behind the panel. The best LCD displays will have wide viewing technology (such as in-plane switching) and you should definitely screen-test the latest OLED panels. Not only are colours super vivid and high-speed action jitter-free, they use less power than traditional screens, though usually at the expense of some brightness.
The next step is capturing HD video. While many phones now boast 720 or even 1080 movie modes, there can be huge differences due to their optics, exposure and processing. Look for autofocus and an LED video light to get the best from your clips -- and don't forget the importance of audio. It won't be 5.1 surround, but stereo adds atmosphere and almost always sounds better than a single microphone.
Whether you're watching home movies or Hollywood blockbusters in HD, you'll need plenty of on-board storage. Internal memory is easy but a convenient card slot means you'll never run out of room. A replaceable battery is a real plus point, too, especially when your phone starts to fade out halfway through a long plane journey.
Finally, what's the use of high definition? The best mobiles make sharing HD content simple. Wi-Fi phones that are DLNA (Digital Living Network Alliance) compatible will be able to wirelessly stream vids direct to other DLNA devices, including computers of course, but also some cool new flat-screen TVs. For an easier and less geeky alternative, a few handsets offer HDMI output, usually in the form of a mini-HDMI socket and cable, although sometimes you'll need to buy an overpriced plastic dock.
Put on your HD specs and tune in to some of the best new high-def-friendly phones below.