T-Mobile was quick to tout its own success with Wi-Fi calling after AT&T (NYSE: T) noted its customers' uptake of the technology earlier this week.

Bill Smith, AT&T's president of technology operations, told attendees at an investors conference Tuesday that the carrier is routing more than 4 million calls a day over Wi-Fi. AT&T began to offer Wi-Fi calling on newer iPhones last fall, and last week it extended the service to Android users for the first time when it launched it on the LG G4.

"We just recently started turning up Android-based operating systems, so I think that's going to go up tremendously, and we're doing that at extremely impressive performance levels," Smith said, as quoted in FierceWireless' report.

T-Mobile reached out to FierceWireless soon after the story posted to offer its own statistics. More than 6.5 million T-Mobile customers use Wi-Fi calling on a monthly basis, the carrier said, and nearly 44 million devices on its network support the technology.

T-Mobile CTO Neville Ray piled on, taking to Twitter to boast that the operator sees 22 million Wi-Fi calls per day. "@ATT so cute you do 4M WiFi calls," Ray tweeted.

As Smith said earlier this week, increasing uptake of Wi-Fi calling bodes well as traffic continues to ramp up, forcing carriers to look to unlicensed spectrum as well as licensed airwaves.

"Unlicensed has to come into the mix when you think about wireless solutions," Smith observed. "About 80 percent of the wireless traffic today is handled over Wi-Fi networks, so we're actually pretty bullish about how we take not only Wi-Fi but other unlicensed bands. And if you build a control plane that is sophisticated enough to manage that effectively, it can really help you…. So when you consider that this has been kind of an un-engineered asset that we've been taking advantage of, I think when you look going forward we will be sophisticated enough to use unlicensed bands more effectively and in a more sophisticated manner."

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