There are an estimated 3 billion smartphone users worldwide.

Over the past decade, we've seen phones get larger, faster and loaded with more features

like fingerprint technology, improved cameras and digital assistants.

But the pace of innovation is slowing.

And smartphone sales are declining.

Manufacturers are scrambling to find new ways to conjure up excitement.

This is your Bloomberg QuickTake on the future of smartphones.

In 2007, Apple's iPhone ushered in the modern era of smartphones.

At the time, text messages and slow data were about all most wireless networks could handle.

Then carriers moved to 4G, download speeds got faster,

phones got more sophisticated and growth exploded, surging 40% in 2013.

But 2017 saw the first contraction -

and the trend continued into 2018.

Devices aren't making the big, innovative leaps they used to.

Phones are also getting more durable.

And some of the biggest markets for smartphones are reaching saturation.

Most Chinese have a smartphone now.

So what will be the next growth driver?

Some of the world's biggest smartphone makers seem to think it will be the foldable screen,

which doubles the size of the display without making the phone gigantic.

Companies like Samsung, Huawei and Xiaomi are betting on it, but the technology isn't quite there.

In April, Samsung had to delay the launch of its new foldable phone

after some early users of the $2000 Galaxy Fold reported that it failed after only a few days of use.

The screen stopped working after people peeled off a special film that looked just like a screen protector.

It was a pretty devastating blow

so early in the process of releasing foldable phones.

What was unique about the Samsung Fold is it folded inwards, like a book.

Whereas Huawei have brought out a foldable phone that folds outwards,

so the screen is actually on the outside.

What that means is not folding as hard,

not so much of a crease down the middle

as you have on the Samsung phone.

So while companies are experimenting with

how they're going to design these devices,

they might start going more for the Huawei option.

Or maybe the game changer will be 5G

- though its rollout could be slowed by geopolitics and security concerns.

5G networks promise to be so fast

that it would only take a few seconds to download a feature-length movie.

Samsung has released a 5G phone in South Korea and Huawei also has one in the works.

What it will also do is support all the other technology that's emerging.

For driverless cars to work, the world is counting on the capacity for wireless networks to carry that data.

For the Internet of Things to work, which allows you to connect your fridge to the internet

or remote control the lights in your house when you're not there,

that requires a lot of bandwidth, a lot of data.

But experience has shown that

it usually takes more than one improvement to get people to shell out for an upgrade.

Even when we went from 2G to 3G to 4G,

it was a combination of things.

The ability to download the data made all these extra uses by the consumer so much more possible.

But not everyone uses their phone the same way.

So what you need to see is a capacity for people to start using their phones

in new and different ways to justify spending more money.