2019 was a hell of a year for phones, but in many ways, it was just setting the stage for the top trends that will continue to dominate 2020. Devices like the rumored Galaxy S11 and Huawei P40 Pro have the chance to bring dramatic changes to an industry that was widely considered stagnant this time last year. Since then, we saw the first 5G phones that can command wildly high data speeds and foldable screens that bend in half. 

2019 is now historic for introducing the Samsung Galaxy Fold, Huawei Mate X and Motorola Razr flip phone. We also saw less flashy, but equally important themes of longer-lasting and faster-charging batteries, operating systems added new bells and whistles (dark mode!) and digital assistants got smarter. Phone cameras embraced new sensors and enhanced image capture, from seriously impressive periscope zoom technology to astrophotography in the Pixel 4.

Looking forward, we'll see these features beefed up and gain new tricks -- cameras with oodles of megapixels, phones with outrageously large batteries and screens that give you smoother graphics. We'll see more 5G in more phones. We'll also get some clarity over the role of foldable phones, if they have one at all beyond this fascinating period of experimentation.

Here are the most important things you have to look forward to with this year's phones.

5G becomes more mainstream in 2020

5G networks kicked off in 2019, and at least a handful of phones had to be there to support them. Most of these devices were variants of premium models, with boosted price tags and limited 5G networks to work with. 

There were a few success stories. This past September, Samsung said it sold 2 million 5G phones in its home country of South Korea, and some brands worked on cheaper 5G phones like the $520 Xiaomi Mi 9 Pro. But on the whole, there was much ado about nothing, especially since the chips inside aren't terribly efficient yet and tend to chew through battery when you're actually using a 5G connection. 

5G phones also have a tendency to overheat when it's hot out, with the 5G connection shutting down to keep the phone from reaching dangerous internal temperatures.

Despite 2019's growing pains, 5G is still inevitable. In countries where carriers are building out their 5G networks, expect every premium phone to be either 5G-ready or have a 5G variant. For example, Samsung's Galaxy S11 could be one of the first to bring 5G to many more people. 

Once 5G networks become more widespread, phones will be able to access significantly higher data speeds and more responsive service, which could mean:

• Lighting-fast downloads of large files, like Netflix shows to watch offline.
• Seamless video calls.
• Amazing graphics on streaming real-time games and AR experiences.
• A split-second advantage in responsiveness when shooters like Fortnite.

Get to know the different flavors of 5G -- and which real-world benefits will actually come to you. And here's why the first cheap 5G phones may not be very good.

Foldable phones get real

If 2019 was the year of seeing foldable phones come to life, then 2020 is about determining if phone screens that bend are a potential future or a gimmick destined to be forgotten like 3D displays. 

Samsung, Motorola and Huawei have launched foldable phones that work, each with their own design. The Galaxy Fold gives us a book design that opens into a tablet. The even larger Mate X has one big wraparound screen around the outside of the device, which can be used three different ways. And the Motorola Razr is a small phone flips up vertically to reveal a tall, narrow display within.

Foldable phones seek to give you a larger screen in a much smaller body. In 2019, they're expensive, ranging from $1,500 for the totable Razr to over $2,000 for the Galaxy Fold and roughly $2,400 for the Mate X.

That's at least 50% more expensive up front than you'd spend on a premium superphone, like the $1,000 iPhone 11 Pro. Consider, too, that foldable phone screens are made of plastic, a more fragile material than glass. They're more prone to scratches and damage from too much direct pressure.

We know that the Fold, Razr, and Mate X will get company in 2020 and beyond. Phone-makers like LG, Xiaomi and TCL have been vocal about experimenting with foldable designs, like this foldable device that bends in three places to open into a 10-inch tablet. 

Samsung already teased a new foldable in the works, a vertical flip phone reminiscent of the Motorola Razr. Rumors also suggest that Samsung is working on the Galaxy Fold 2 for August 2020.

Photography continues to rise

Camera quality is one of the top three reasons people buy one phone over another, alongside screen preference and battery life, according to a consumer study by research firm Kantar Worldpanel.

Mobile phone photography made deep strides in 2019, with advancements in telephoto quality and advanced image processing. For example, telephoto and/or wide-angle sensors have now become standard for high-end phones. The Huawei P30 Pro is notable for its periscope lens that achieves incredible zoom results using a combination of optical and digital zoom.

Phone brands are also using sophisticated sensors and post-processing to achieve shots that were previously only achievable on DSLR cameras. The standout was Google Pixel 4's astrophotography mode, which is capable of taking sharp photos of the starry sky, assuming you're in a dark enough place to begin with. It's astounding.

In 2020, new phone processors will be able to support up to 200-megapixel cameras, and advancements will come to telephoto and ultra-wide angle photography, particularly with more top-tier phones using 5x optical zoom. Slow-motion and high-resolution video will also get a boost, thanks to more powerful processors.

Whoa. Once you get to the right place, you *can* take astrophotography photos with @madebygoogle Pixel 4. This was in New Mexico, very cold 10°F with clear air, the Orion constellation above juniper trees lit faintly by my sister's bedroom light. 4 minutes of combined exposures. pic.twitter.com/esBSfDECb8

— Stephen Shankland (@stshank) December 30, 2019

120Hz screens come to the masses

Screens on high-end phones will continue to be crisp, detailed and saturated with color. But also expect them to get "faster," with refresh rates of 120Hz -- the Galaxy S11 is rumored to build the feature in.

The standard refresh rate is currently 60Hz. That indicates the number of times the images on your display update per second. So, 60Hz equals 60 refreshes, and 120Hz equals 120 refreshes per second.

A faster refresh rate makes graphics look smoother, which is important for fast-paced and graphically heavy games. But It also enhances graphics for 4K video, screen animations and even scrolling through a web page or your app drawer.

A high refresh rate could also help improve the detail or responsiveness of AR graphics, an area that's got a lot of potential, but is mostly used in games right now, like Pokemon Go, Minecraft Earth and Harry Potter: Wizards Unite.

Right now, only a handful of phones have 90Hz or 120Hz screens built in, like the OnePlus 7T and Google Pixel 4. The setting is optional, because increasing the screen refresh rate by 50% (90Hz) or 100% (120Hz) takes a toll on your battery.

Fast charging will get faster

Your phone is only as good as its battery, because if it runs out of charge, or you're dashing for the nearest outlet, then your phone's no good to you. 

A bigger battery that holds more charge is one solution. Fast-charging is another. The idea is that if you can't get everything you need out of your battery, you can at least give yourself most of one in as little as 30 minutes.

For example, the Galaxy Note 10 Plus comes with a 25-watt charger that fills up your empty battery in about an hour. It also works with a 45-watt charger that fills your battery up in half the time.

Apple, too, embraced fast-charging in 2019, with an 18-watt charger in the box for the iPhone 11 Pro and Pro Max. 

So it's pretty inevitable that fast charging and battery maintenance are going to become even more of a hot topic in 2020. The fastest fast chargers will start showing up as a matter of course, and we could potentially see Samsung start including 45-watt chargers in the box for its most expensive phones. 

At the very least, we might see Apple and other rivals try to close the gap with Samsung's 25-watt charger by introducing their own. Until we see how it all shakes out, here are six truths about fast charging and your phone's battery life.

High-end phones get more expensive

Phone prices have been on the rise in the last several years, with new camera features and larger screen sizes used to justify the hike in cost.

Enter 5G, foldable phone designs and even more camera, battery and processor enhancements and it's clear to see that prices will only go up, at least on the high end. We'll always see more moderate pricing for midrange phones, especially those that use older technology. 

Phones that are 4G-only, or which use a midrange 5G processor like the Snapdragon 765 chipset will also be able to dodge the steepest costs. But on the whole, expect 5G phones to cost more than 4G phones with the same parts. Also expect that affordable 5G phones will downshift specs in exchange for 5G support -- and they might not be all that good.