Update 15 March: The Galaxy S4 has now been announced. You can read our S4 hands-on here, keep track of the UK pricing and availability here, see how the S4 compares to the iPhone, Lumia 920, HTC One and Nexus 4 here, read what's changed over the S3 here and what we didn't get here. We have replaced the video above with our preview from the launch event in New York and left the original article below.
The Samsung Galaxy S3 is only nine months old, but that's a long time in gadget years. Now our gadget-addled minds are turning to what Samsung has planned for its fourth S-series mobile.
Such is the merry march of progress, and as time stands still for no man (or mobile), here's everything we're expecting to see from the Galaxy S4, including news, specs and an educated guess at possible release dates.
14 March reveal
We don't have long to wait now, as Samsung has confirmed that the Galaxy S4 will be unveiled in an event in New York on 14 March. That's right folks, we only have days to wait before we get our eyes on the next Galaxy mobile.
What will the Galaxy S4 look like?
The Samsung Galaxy S3 looks very different to 2011's Galaxy S2, with a luxurious curved style that was a marked departure from its blocky predecessor. As such, it's hard to guess what the Galaxy S4 will look like, but there are a few clues to be gleaned.
5-inch, 440ppi screen?
The 5.5-inch Galaxy Note 2 has proved popular, so expect to see Samsung increase the display real estate from the S3's 4.8-inch screen.
Samsung recently dropped a massive hint that an as-yet-unnamed phone with a 5-inch, 1080p display is on the horizon, due to be revealed within the first three months of the year. Samsung's saying that panel will have 440 pixels per inch, which would beat the iPhone 5's 326ppi when it comes to packing in the pixels.
Recently-spied screenshots suggest the Galaxy S4 will play host to eye-monitoring technology, with a front-facing camera that keeps an eye on your ocular units. This will enable features like Smart pause, which automatically pauses video when you look away from the screen, and Smart scroll, which starts a page scrolling when you're looking at the screen.
No screen is truly unbreakable of course, not even those hovering shield screens they fight with in Dune, but rumours peg Samsung to be filling the Galaxy S4's screen with plastic substrate that will battle cracks and scratches, even if the phone takes a nose dive onto your patio.
No home button?
The S2 and S3 have both featured a physical home button underneath the screen, even as other mobiles such as the HTC One X or Samsung's own Galaxy Nexus ditch a central key in favour of touch-sensitive options.
I wouldn't be surprised to see Samsung keeping existing Galaxy owners satisfied by sticking with the home button, though a recent leaked snap that purportedly comes from within Samsung and shows the S4 is conspicuously lacking a home key.
Samsung has an almost unhealthy obsession with creating smart phones that are as thin and light as possible, which is why even the physically huge Galaxy S3 feels like a helium-filled dove when you grip it in your hand. The Galaxy S2, Galaxy Note and Galaxy Note 2 are all eerily thin and light too, so count on Samsung's next flagship phone being even skinnier, and weighing practically nothing.
Unless miracle materials are discovered deep within the Earth's crust or mined from asteroids within the next year, that means the Galaxy S4 will probably be made of plastic, like the S3. Plastic is divisive among tech fans -- some enjoy the light, airy feeling, while some prefer the robust build quality that comes with a sturdy metal case.
Samsung recently showed off its 'Youm' flexible display technology, which lets a display wrap around a phone's casing -- check out the video embedded below to see it in action.
While this technology is a tempting glimpse at the near future, I'd be surprised if Samsung chose it for the Galaxy S4, as it's likely to still be very expensive. The thought of a high-end smart phone with a wrap-around display certainly tickles our fancy though -- no harm in hoping, eh?
Both the S2 and the S3 sport 8-megapixel cameras, and while they're both decent smart phone snappers, the thought of beefing that sensor up to one that's a little more potent is a welcome one.
Rumours to that effect have emerged, and it wouldn't be the most outlandish development, but we'll still need to wait until we have it in our hands before we know for sure how decent a camera the next Samsung flagship will possess.
So what about some kooky new tech? Holographic interface? Built-in fishbowl? The ability to turn into liquid and flush down a toilet?
All sorts of weird and wonderful features are bound to be rumoured for the Galaxy S4, but to be honest I expect Samsung will play it safe with its most important mobile, and release a bigger, more powerful smart phone -- the kind of procedural improvements we've seen Apple make with the iPhone 5.
As mentioned above, we know that Samsung is keen on flexible displays, and I've seen some of the company's transparent LCD panels, which are mouth-wateringly delicious. I'd love to see some of this wacky technology inside a new smart phone, but I think Samsung is likely to trial any especially unusual new features in a separate phone entirely -- see the projector-sporting Galaxy Beam, for instance.
In 2013, rival operators O2, Vodafone and Three are joining the 4G fray, so a big question for phone shoppers this year will be which smart phones support the speedier browsing speeds 4G provides.
If the Galaxy S4 works across all the major UK operators' 4G spectrum bands, that'll be a major selling point, especially as that's not something the iPhone 5 can currently claim (Apple's latest mobile will so far only work with EE's 4G in the UK).
My guess is the S4 will work across UK networks, seeing as Samsung already has the S3 LTE, which will work on every network, including the ones that aren't even set up yet.
Android Jelly Bean or Key Lime Pie?
Android 4.2 Jelly Bean is the latest version of Android, though current Samsung devices like the Galaxy S3 are running Android 4.1 Jelly Bean, a slightly earlier version that's missing a few features.
If the Galaxy S4 comes out at the end of May (which is when the S3 went on sale) I'd wager it's likely to be running Android 4.2 Jelly Bean. Like the confections they're named after, however, Android versions never stay fresh for long, and the follow-up to version 4.2 is already being spoken of. In keeping with Google's alphabetical naming conventions, it's rumoured to be dubbed Android Key Lime Pie.
I think we're unlikely to see Key Lime Pie arriving with the Galaxy S4, as Google usually chooses Nexus devices such as the Nexus 4 to debut a fresh version of Android.
Based on Google's history, I think it's more likely the Galaxy S4 will land running Android Jelly Bean 4.2, before getting updated to Key Lime Pie (or Kendal Mint Cake or Kellogg's Rice Krispie Cake or whatever it ends up being called).
Samsung is sure to opt for its own TouchWiz Android skin once more, so don't expect to see a vanilla version of Google's operating system powering the S4.
How about the name?
Tech companies are notoriously slippery when it comes to tech naming conventions ('new iPad', anyone?), but Samsung will want to trade on the positive vibes surrounding its Galaxy branding as much as possible. After the S2 came the S3, so for now at least S4 would seem to make sense.
To be totally accurate, the S II and S III have struggled along with Roman numerals that everyone has ignored, so it may well be the S IV, although that sounds like something you'd find in a hospital. Teaser posters that popped up in New York bear a numerical '4', so it looks like Samsung is ditching the numerals at last.
When will it come out?
The big question: when can you buy the Galaxy S4? Well, based on past form, expect Samsung to put the S4 on sale roughly a month after it's announced. That would suggest a mid-April launch.
That would be less than a year after the Galaxy S3 went on sale, which could annoy anyone who recently bought the S3 assuming it would stay cutting-edge until the summer. Perhaps Samsung wants to get more of a head-start on whatever Apple has up its sleeves later this year.
Stay tuned, and let me know what you'd like to see from the Galaxy S4 in the comments below, or on our Facebook wall.
Update 17 January: Latest rumours added.
Update 8 March: More rumours and announcement date added, as well as video.