T-Mobile will begin rolling out its 5G network across the country this week, taking the first steps toward ultra-fast next-generation wireless technology. The Bellevue, Wash., wireless carrier says 5G service will be accessible to 200 million Americans starting Dec. 6.

T-Mobile is also opening up pre-orders for two 5G-enabled devices this week, the Samsung Galaxy Note10+ 5G and the OnePlus 7T Pro 5G McLaren. The phones have capacity for 4G LTE and 5G service.

The 5G network T-Mobile is lighting up on Dec. 6 won’t deliver the lightning-fast speeds that have generated so much buzz around next-gen wireless. That faster iteration of 5G relies on millimeter wave technology, which requires a high number of small cell antennas to deliver service.

The initial rollout will focus on blanketing larger number of customers through low-band frequency that is slower than millimeter wave, but has a greater reach. It will serve as the “foundational layer” for 5G, Mark McDiarmid, T-Mobile’s senior vice president of network technology, said in an interview with GeekWire.

“We’re super excited about this network step,” he said. “It’s not the last step we’ll make with 5G. It’s just the beginning and we’re excited about the competition that T-Mobile brings to the marketplace.”

Though it’s faster, millimeter wave 5G comes with some challenges. Building out the infrastructure is a heavy lift and the higher frequency doesn’t cover as much area and can have trouble penetrating buildings and other objects. It can also be difficult to secure the necessary permits to build out small cell infrastructure in cities, as some carriers are learning in Seattle.

Low-band 5G is incrementally faster than 4G and more reliable than millimeter wave 5G over long distances. T-Mobile estimates customers who upgrade to the new 5G phones will see an immediate 20 percent lift in wireless service performance when the carrier rolls out the first phase of its network this week.

“The starting point is not 5G versus 4G,” McDiarmid said. “The starting point is 4G plus 5G, because the two networks work together.”

The mega-merger with Sprint is key to T-Mobile’s 5G plans. Should the deal be approved, the “New T-Mobile” will be able to leverage Sprint’s mid-band spectrum to deliver another bump in speed as soon as next year, closer to the gigabit range that has long been promoted as part of 5G.

By 2024, T-Mobile estimates its wireless service will be more than 10 times faster than current speeds. T-Mobile is publishing maps that allow customers to see whether they have 5G coverage along with the announcement.

T-Mobile says all three types of 5G will eventually be part of its long-term service. The company recently spent approximately $800 million on additional millimeter wave spectrum to bolster its network.

T-Mobile is locked in a tight 5G race with competitors AT&T and Verizon. Verizon’s 5G network is available in 18 cities, with plans to reach 30 cities by the end of the year. Verizon has been mocked by competitors, including T-Mobile, for relying too heavily on millimeter wave technology, meaning its 5G network can’t reach large swaths of customers and isn’t effective inside buildings.

AT&T is taking a similar approach to T-Mobile, relying on low-band spectrum to build out a “nationwide” 5G network the company hopes to launch in the first half of next year. AT&T’s first 5G offering came in late 2018, a millimeter wave hotspot for select business customers. Last month, AT&T opened its burgeoning 5G network up to consumers for the first time, starting with five cities and plans to expand to 10 more soon.

T-Mobile executives said Verizon and AT&T have relied too heavily on millimeter wave so far, failing to build a solid 5G foundation. They compared it to lighting up a series of sparkly birthday candles without first baking a cake.

While carriers are moving fast to establish early leadership in 5G, there aren’t many options for next-generation phones yet. Companies like Samsung, OnePlus and Huawei have all announced multiple 5G phones. But others, like Apple and Google, have yet to reveal next-generation devices.

The Samsung Galaxy Note10+ 5G and the OnePlus 7T Pro 5G McLaren, the first two 5G phones in T-Mobile’s 5G network, retail for $1,300 and $900 respectively. T-Mobile says it won’t charge customers extra for 5G service, and the new 5G phones can be paid off in monthly installments, just like any other T-Mobile phone. The Note10+ 5G will cost customers $36.12 per month for 36 months, and the OnePlus plan is $37.50 per month for 24 months.

5G has been the next big thing in technology for years now, promising faster speeds to underpin self-driving cars, superior virtual and augmented reality, smart cities and more. The standards for 5G are set by a group called 3GPP, which was originally established to create the ground rules for 3G. Speed is a component, but the standards for 5G include a huge number of technical specifications as well.

Critics claim that the marketplace will become less competitive if T-Mobile’s mega-merger with Sprint is allowed to go through. But the companies say that the deal will help them improve wireless service, particularly to rural and underserved communities.

T-Mobile is eager to add Sprint’s mid-band spectrum to its 5G service if the two companies are allowed to combine. They’ve received clearance from federal regulators but a multi-state lawsuit casts some doubt on the deal’s future.