According to new data from wireless monitoring company OpenSignal, mobile customers aren’t using Wi-Fi as much as they used to. The firm attributed the trend to the fact that all of the nation’s wireless network operators—Verizon, AT&T, T-Mobile and Sprint—have been pushing unlimited data plans for more than a year now.

“Not surprisingly, our data, which covers the 90 days from December 1, 2017, shows that time on Wi-Fi has fallen across three out of the four major operators,” wrote OpenSignal’s Peter Boyland on the company’s blog. “But more notable is the fact that the ‘big two’ AT&T and Verizon saw the greatest drop in our measurements. As unlimited data plans in the U.S. become more ubiquitous, customers appear less concerned about finding a ‘free’ Wi-F connection, leaning more on their ‘unlimited’ 3G and 4G networks for connectivity.”

Specifically, OpenSignal reported that, when compared with the same period last year, Wi-Fi usage as a percent of customers’ overall time largely declined:

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AT&T’s fell to 49% from 52%.

Verizon’s fell to 51% from 54%.

T-Mobile’s fell to 41% from 43%.

Sprint stayed steady on 51%.

The firm noted that T-Mobile and Sprint have long offered unlimited data options, but T-Mobile has been pushing its unlimited T-Mobile ONE plan particularly hard in recent months. And Verizon and AT&T joined the unlimited game early last year, so the carriers’ customer usage now appears to be changing as a result.

Interestingly, OpenSignal said that after AT&T and Verizon launched unlimited data options, the firm’s data showed that both carriers’ 4G speeds fell. “But the big two are now recovering, with Verizon now back to its pre-unlimited plan levels, according to our data,” Boyland noted.

OpenSignal derives its data from applications installed on wireless customers’ handsets that monitor their usage.

OpenSignal’s data on Wi-Fi usage largely dovetails with similar data from Strategy Analytics’ AppOptix service. Recent data from that firm’s report shows that customers with an unlimited data plan used an average of roughly 12 GB of Wi-Fi data during the month of February and around 5 GB of cellular data.

Article updated April 20 to clarify OpenSignal's data.