Wireless carriers spent much of 2017 talking about 5G, but at the same time they were busy investing in LTE. OpenSignal's latest speed test report shows average speeds increasing for all four nationwide carrier networks, even as the reintroduction of unlimited plans sent data usage skyrocketing.

OpenSignal, which collects its data from a smartphone application that users choose to download, reports that by the end of last year all four nationwide carriers were delivering more than 10 Mbps on average. That average includes the speeds users get on legacy networks when LTE isn't available.

T-Mobile dominated the OpenSignal speeds tests throughout the year, starting off just slightly ahead of second place Verizon, then widening its lead significantly after Verizon followed T-Mobile's lead by launching an unlimited data plan. By the end of the year, the gap had narrowed again.

Sponsored by Southco Inc. How To Secure 5G Equipment With Electronic Access Learn how to protect small cell enclosures from physical threats and deliver better, stronger and more reliable networks with electronic locks and access control systems. Read the Article

Verizon and AT&T both started offering unlimited data plans last year, and both saw their average network speeds decline as a result, according to OpenSignal. Over the course of the year, investments in the networks helped the two largest carriers meet their increased demand and network speeds were back up by the end of the year.

RELATED: Thanks to unlimited data, wireless users are increasingly eschewing Wi-Fi

Verizon often bills its network as the fastest in the U.S., citing data collected by another firm, RootMetrics. RootMetrics gathers data by issuing smartphones to testers, rather than collecting the data from a mobile app like OpenSignal does.

OpenSignal consistently found Verizon to have the second fastest network in 2017, with AT&T and Sprint a distant third and fourth. LTE availability impacts the OpenSignal ratings because when people can't get LTE they fall back to slower legacy networks. For example, AT&T scored points by significantly increasing LTE availability last year, and even though its average LTE speed went down, average network speed rose as more people moved from 3G to LTE.

Not surprisingly, Sprint users started to report faster speeds towards the end of the year, not long after tower companies began to report more investment and activity from the carrier. Sprint says it continues to invest heavily in its network, despite the possibility that a merger with T-Mobile will radically alter the company's future.

Even the fastest network speeds reported by OpenSignal (about 18 Mbps) sound slow in comparison to the gigabit-per-second speeds the carriers are predicting in the near future. These speeds are expected with LTE-Advanced, and of course with 5G. That doesn't mean data collected from smartphone users will start showing average network speeds of a gigabit-per-second anytime soon. But LTE-A network features like carrier aggregation and massive MIMO are expected to boost speeds even for users whose phones can't take advantage of those technologies. That's because they make the network more efficient, which benefits all users.