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Mobile subscribers who upgrade to one of the expensive, new 5G compatible phones may find the experience more than a little bit frustrating, at least for now, according to a new report from research firm Opensignal.

Download speeds vary widely, though they are typically faster than the average 4G download, Opensignal says in the report. But coverage is also extremely uneven, even in the cities where the carriers say that they have installed 5G.

“All of the 5G speeds we see are fast by U.S. standards, but seeing a 5G icon on the screen is no guarantee of 5G,” Opensignal analysts Francesco Rizzato and Ian Fogg noted in a blog post accompanying the results.

Verizon, AT&T, and T-Mobile are spending tens of billions of dollars to add 5G. But it will take several more years before the superfast technology, which can theoretically offer download speeds 10 to 100 times faster than an average 4G connection, are widely available.

Additionally, customers must upgrade to 5G compatible phones, which currently cost at least $1,000, though lower-priced models should hit stores in coming months. The faster connections will also eventually bring new applications, like mobile virtual reality games and multi-angle live sports broadcasts.

In Opensignal’s report, actual results depended on the type of 5G that each carrier has deployed in their networks. Verizon is currently relying on 5G in high-frequency bands, known as millimeter wave, that carry vast amounts of data but don’t travel too far. Meanwhile, for consumers, AT&T is using lower bands, just like those used for 4G, that travel farther but carry less data (AT&T says it will add millimeter wave for consumers next month when some new Samsung phones become available). T-Mobile is using both approaches.

The bottom line is that Verizon provides the fastest average download speeds but the smallest coverage area, according to Opensignal. Connections on Verizon’s 5G network averaged 723 megabits per second, fast enough to download a high-definition movie in a few seconds, the report says. But such coverage was found only 5% of the time—even in the downtown areas of the 31 cities where Verizon installed the new technology, Opensignal says. Verizon says it will reach 60 cities by year end.

AT&T, which has reached over 30 cities so far, averaged 59 Mbps speeds and 11% availability in the cities where its consumer service is available.

T-Mobile’s higher-speed network offered download speeds averaging 243 Mbps and availability 11% of the time in the six cities where it is available. In a much larger area covering most of the country, T-Mobile’s lower-frequency and lower-speed 5G network averaged just 48 Mbps downloads, requiring five to 10 minutes to download a movie, but it was available 53% of the time.

Sprint, which is about to be acquired by T-Mobile, is using a hybrid approach to 5G in nine cities. Its network averaged download speeds of 243 Mbps and was available 47% of the time in downtown areas. But T-Mobile says it will reallocate that spectrum to be used in its 5G network once the $26 billion merger is completed.

The overall findings from Opensignal are consistent with what Fortune found its own recent tests.

All 5G phones revert to using 4G networks when they cannot find a 5G signal. So Opensignal also reported on the best combined experience for the phones.

Verizon’s 5G phone still topped the list, averaging 85 Mbps for all downloads on 4G and 5G networks. T-Mobile was second at 59 Mbps and AT&T was third at 52 Mbps.

Opensignal collects download and connection data from apps installed on tens of millions of consumers phones, rather than by driving around with its own test phones, as rival Rootmetrics does. The crowd-sourced data provides many more measurements but without the same exact comparability of its rival’s more planned phone tests.

Here’s how wireless carriers rank on 5G speeds, according to report

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