Remember Moto Mods? Motorola’s accessory series allowed people to snap everything from bigger speakers to battery packs was one of those neat ideas that didn’t quite catch on.

Reports suggest it’s back… and might come with a killer feature: Support for 5G networks.

It’s a neat solution to a tricky problem. Carriers in the US promised to bring super-fast 5G to smartphones as soon as later this year. So if users want to take advantage, they’ll need new devices that can handle the higher-frequency signals. But it’ll take a while for 5G to roll out, so not everyone needs it right away.

The Moto Z3 is set to be unveiled on Thursday, but who needs to wait when we’ve got leaks? (Picture: Android Headlines)

The new mods are supposed to be compatible with the latest flagship from Lenovo’s Motorola: The Moto Z3. It’s not being unveiled until Thursday, but Android Headlines already showed us what it’s supposed to look like. Other than not having a fingerprint scanner on the chin or the back, the outside seems pretty standard.

The real headline (and indeed the headline of this story) is the snap-on accessory that makes the Moto Z3 5G-ready. Photos obtained by XDA Developers show the phone case has a nub on top that likely houses an antenna.

I know “what’s old is new again” is a thing but I really didn’t expect the antenna nub to return. (Picture: XDA Developers)

So… why do we need that extra, retro-looking antenna? Well, here’s the thing: 5G is dramatically faster than 4G because it relies on so-called mmWave, which has a higher frequency than radio waves, providing more bandwidth.

But mmWave comes with some downsides too. It doesn’t travel as far. It can also be blocked by walls -- or even just your finger covering the antenna.

To overcome that, one solution is to have the antenna protrude outside the phone body -- just like an old school cell phone from the 1990s.  

It might not be the only solution though: Qualcomm says that it has a more sophisticated setup. Its new antenna module claims to include four antennas, each pointing towards different directions to maximize signal coverage. Smaller than a penny, the QTM052 is designed to fit inside a phone’s bezel.

In the end though, a 5G smartphone won’t be able to deliver ultra-quick speed without a 5G network. That means carriers will have to build lots of new 5G towers across each city -- enough to compensate for mmWave’s short range and weak penetration.

AT&T has said it plans to make mobile 5G available in Atlanta, Dallas and Waco, Texas this year. Verizon, which could be the Moto Z3’s exclusive US carrier, told CNBC it expects a rollout early next year. Sprint’s services are also expected to come out nationwide in 2019, followed by T-Mobile in 2020.