Mobile World Congress might have you convinced of two major mobile trends for 2019: foldable phones and 5G.

Foldable phones are undeniably interesting — we finally have real phones that transform into tablets with larger screens! — but 5G, the next generation of faster and more reliable cellular connectivity, has the potential to truly change how we live and work, even if foldable phones end up becoming a fad.

At MWC 2019, companies from all corners of the globe tripped over each other to showcase a near future where high-resolution movies will download in seconds, expansive 3D games and VR will be streamed directly to phones and new headsets, and smart cars (self-driving or not) will be able to recognize each other to prevent collisions.

I'm 100 percent onboard with these 5G promises, but there's one thing people are overlooking: data plans.

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It's stupid easy for a company like Huawei to boast about how its Mate X foldable phone will be the "world's fastest 5G foldable phone" when it launches in June and how the device's Balong 5000 modem will be able to download a 1GB movie in three seconds.

Doing the math, it would mean the Mate X pulling down 333 MB/s to complete the download. That's impressive... assuming you can first hop on a 5G network (most of them are still in the very early phase of deployment and won't have proper launches until 2020 at the earliest). But gobbling so much data so quickly will eat into your data plan significantly faster than before.

Consider your current 4G LTE data plan. I'll use myself as an example: I'm on T-Mobile and have 10GB of data per month. As a power user, I'm barely making it work.

Putting aside the question of how much more it'll cost per month to get 5G or how fast a 5G connection will be, if I were to download a 1GB movie, I'd use up 1/10th of my data in three seconds. Then, let's say I want to stream a few 3D games to my smartphone. Surely, that'll chew through a few more gigs — again, within seconds.

If I download 10 movies, each at 1GB each, my 10GB data plan is gone in 30 seconds!

Add on all of videos I upload to Instagram Stories, tweets I send, emails I write, news I read, and YouTube videos I watch on a daily basis and I am certain I'll eat through my data plan in a couple of minutes.

I mean, if I download 10 movies, each at 1GB each, my 10GB data plan is gone in 30 seconds!

Carriers will market 5G to regular folks with a simple message: faster connectivity means you can download and stream more.

But to even get the benefit of this 5G dream, you will need a bountiful data plan that'll support it. As it stands, existing data plans with "ceilings" or "caps" (or whatever you prefer to call them) will not work to sustain the kind of data-hungry applications that 5G promises to deliver.

Unlimited data plans will be the only way for anyone to get the full 5G experience. And that's the problem: No wireless carrier besides T-Mobile has committed to offering unlimited 5G data plans. And T-Mobile's not launching its 5G network until the second half of 2019.

Maybe AT&T and Verizon and Sprint will announce their own unlimited data plans for 5G later this year, but why even consider 5G so soon if they're not willing to share their full plans with everyone today?

We know the answer to that: because 5G isn't ready yet. 2019 is another year many companies will make a lot of noise about how they have 5G phones ready to go, but it's mostly smoke. The earliest 5G will actually be useful to most consumers will be 2020.

When "unlimited" isn't really unlimited

But even if you get an unlimited 5G plan, what does that really mean? All four of the major wireless carriers in the U.S. offer unlimited data plans, but they're not really unlimited.

On T-Mobile, after 50GB of data, the company says users "may notice reduced speeds until next bill cycle due to data prioritization."

Ditto for other carriers like AT&T, Sprint, and Verizon. All of them throttle cellular speeds after you've used a certain amount of data on your "unlimited" plan. I've personally noticed a reduction in data speed from 4G LTE to 3G (or slower) speeds and, my friend, it's brutal when you need a decent connection and aren't aware you've hit your data cap.

Also, even if carriers offer unlimited 5G data plans, how much will it cost us? T-Mobile CEO John Legere has pledged to keep prices the same as 4G LTE for the next three years, which means a single line will cost $70/month until 2022, but what about the other carriers? We just don't know what their plans are.

If history has taught us anything, it's that U.S. carriers are greedy corporations. They'll find a way to squeeze more from customers. And if you're smart enough to read between the lines, you'll know that the next-gen data network was designed from the start to nickel and dime consumers.

Like myself, you might think you can get by with your 10GB (or less) of 4G LTE data per month now, but for 5G applications, it won't be enough. To appreciate 5G, you'll have to upgrade to an unlimited data plan (if you aren't already on one) or pay more for your existing plan depending on your carrier.

One way or another, you will end up paying more for 5G.