Samsung’s new flagship smartphones, unveiled at an event in New York City, include Qualcomm’s (QCOM) latest chipsets that are compatible with gigabit speeds on 4G LTE networks. T-Mobile said it deployed additional technology, including the ability for a phone to transmit over several different spectrum bands at once, known as carrier aggregation, in hundreds of major cities to enable the gigabit speed.

The new Samsung phones “really have all the bells and whistles that we’ve been pushing so hard on,” Grant Castle, vice president of network engineering at T-Mobile, told Fortune. It was a pre-release version of the Galaxy S8–not identified at the time–that T-Mobile used in a December laboratory demonstration of gigabit speeds, Castle said.

While pre-orders start this week, customers will get the Galaxy S8 phones starting on April 21. Under real world conditions, T-Mobile consumers with an S8 likely won’t quite hit gigabit speeds, fast enough to download an entire high-definition digital movie file in under 30 seconds.

With trees and buildings interfering with cellular signals and the realities of cellphone sites being accessed by many phones at once, the speeds will likely be less than a gigabit but typically at least double what customers previously experienced, Castle said. And T-Mobile doesn’t have enough spectrum in every market to allow a phone to combine channels and hit a gigabit.

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But T-Mobile (TMUS) deployed three distinct technologies for reaching gigabit speeds and said the Galaxy S8 is the first handset able to take advantage of all three at the same time. In addition to combining spectrum channels, a technique known as carrier aggregation, the new phone can also use four antennas at once, or 4X4 MIMO technology. And the Samsung gear can access 256 QAM signals, which cram more data over the same amount of airwaves.

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Sony (SNE) has also announced a gigabit-capable phone, but has not disclosed availability yet. At the Mobile World Congress trade show last month, Sony would say only that the new Xperia XZ Premium would come to the U.S. market in “late spring.” The company has not updated that vague timing yet, a Sony spokeswoman said on Wednesday.

The new Samsung phones are also compatible with another technology that T-Mobile and Sprint (S) are deploying called High Performance User Equipment, or HPUE. The technology allows a phone to use more power to broadcast certain signals, effectively increasing the range and capacity of higher-frequency airwave bands. LG’s new G6 phone, announced last month, is also HPUE-compatible.

Sprint announced its HPUE deployment in December, saying that an upcoming flagship phone from Samsung would be among the first to support the technology.

AT&T (T) said the Galaxy S8 also would be compatible with its gigabit efforts that are slowly rolling out. So far the carrier has announced the rollout of faster 4G LTE technologies in Austin and Indianapolis as part of its “5G Evolution” plan. Theoretical peak speeds of 400 megabits per second will rise to gigabit speeds as additional equipment is deployed.

Verizon (VZ) said it is also deploying technologies such as 256 QAM and 4X4 MIMO. It has also widely deployed carrier aggregation as part of its LTE Advanced effort. But Verizon has not made specific gigabit speed claims. “Our version of the device will have all the bells and whistles, including the speed capabilities,” a spokesman told Fortune on Wednesday.

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