When AT&T and Verizon brought back their unlimited data plans earlier this year, there was great rejoicing amongst their customers. The celebration may have been a little too soon because according to new data by mobile network measuring company, OpenSignal, their LTE speeds took a big hit.

OpenSignal measured more than five billion measurements of 172, 919 U.S. smartphones that revealed the average LTE speeds for each network changed noticeably once the big two—Verizon and AT&T—brought back unlimited data. According to the data, Verizon's average LTE speeds dropped from 16.9Mbps down to 14.9Mbps from February to August. AT&T's speeds dropped to 12.9Mbps from 13.9Mbps.

This is being attributed to increased traffic from Verizon and AT&T's unlimited data. It's essentially a traffic jam clogging up their network that is delivering slower speeds to everyone.

The big winner of this news is T-Mobile. Its speeds actually increased from 16.7Mbps to 17.5Mbps, earning the title of fastest LTE speeds of any network. It isn't an apples to apples comparison though. T-Mobile staunchly applies limits on video consumption by capping quality at 720p, relieving stress on its network.

Sprint, the other of the big four carriers, also saw a slight bump in speeds in the data. Its speeds increase from an average of 9.0Mbps to 9.8Mbps, but those speeds still lag far behind the other carriers.