Apple this week unveiled its first iPhones compatible with 5G wireless networks that, theoretically, offer download speeds 10 to 100 times as fast as current 4G LTE. But don’t count on actually getting such zippy service.

In many cities, 5G networks provide much slower speeds. As a result, many people who buy any of Apple’s new phones, from the $700 iPhone 12 Mini to the $1,100 iPhone 12 Pro Max, will have to wait for telecom companies to improve their networks.

Why do 5G speeds vary so much?

AT&T, Verizon, and T-Mobile are spending tens of billions of dollars to add 5G. But the three carriers have made different choices about which airwave bands to use.

AT&T and Verizon are deploying two kinds of 5G. One flavor uses the same lower-frequency airwave bands that cell phones have always used. Signals in these lower bands travel relatively long distances, making the networks broadly available to hundreds of millions of customers. Unfortunately, those bands are also already crowded with 4G users, and the carriers lack spare capacity. In fact, tests have found that 5G connections via lower bands aren’t much faster than 4G, and, in some cases, are even slower.

But AT&T and Verizon are also using some ultrahigh-frequency bands, also called millimeter wave bands, for 5G that haven’t typically been used for cell phones. These bands can carry huge amounts of data and provide very high speeds, but don’t travel far. As a result, the millimeter wave networks are limited to only parts of a few dozen cities (55 for Verizon and 35 for AT&T).

T-Mobile, meanwhile, has a three-pronged 5G strategy. The carrier has a nationwide low-band network like its rivals and, additionally, has deployed millimeter wave in a few cities. But after buying Sprint this year, T-Mobile gained access to some extra airwaves in a mid-band frequency that better balance availability and speed. So far, T-Mobile’s mid-band network is available in areas where just 25 million people live, but the carrier expects to reach 100 million people by year-end.

The federal government plans to auction more mid-band spectrum later this year, which could help AT&T and Verizon catch up if they win licenses up for bid. Craig Moffett, an analyst with MoffettNathanson Research, said that only then will AT&T’s and Verizon’s 5G be much speedier than their 4G in most places. Until then, he said, “T-Mobile is well out in front.”

What speeds can I expect with a 5G iPhone?

As explained, the download speeds on a new 5G iPhone will depend on the type of network used. On the carriers’ low-band 5G networks, speeds may reach 50 to 100 megabits per second, comparable to 4G and fast enough to download a new music album almost instantly, but requiring five or 10 minutes for a high-definition movie.

On T-Mobile’s mid-band 5G network, a movie may take a minute or two to download. And on a millimeter wave 5G connection, it could take just a few seconds.

What else can I use 5G for besides downloading movies?

Ten years ago, before streaming music and video were ubiquitous, people needed to download much of their online entertainment. But today, downloading entertainment is almost unnecessary.

Apple and the carriers, therefore, have tried to emphasize a few other potential uses for 5G. The most practical is real-time, multiplayer video games like League of Legends (which Apple demonstrated at its iPhone event) or Fortnite (which isn’t currently available in the iPhone app store owing to a legal dispute). That’s because, in addition to providing fast download speeds, 5G also provides quicker connectivity with less lag. Gamers need that kind of low-latency to match people playing on wired home Internet connections.

In the future, real-time virtual reality gaming or conferencing may be a big selling point for 5G because it would allow for creating more realistic-looking environments. Furthermore, Apple is pushing other data intensive ideas, like doctors sharing high-resolution medical scans and architects sharing augmented reality architectural mock-ups of buildings over their phones.

But the bottom line is that even when consumers can get a superfast 5G connection with a new iPhone, they may not notice much of a difference. As Barclays analyst Tim Long wrote after watching Apple’s announcements during an online event on October 13: “We don’t feel the event effectively demonstrated why consumers need 5G for their iPhone.”