After seemingly endless regulatory hurdles at the federal and state levels, T-Mobile announced today that it has completed its merger with Sprint, a deal it says will result in a “transformative 5G network” for consumers and businesses. As previously reported, the merger’s completion marks the end of John Legere’s tenure as T-Mobile’s CEO and the beginning of Mike Sievert’s control over the third-largest U.S. cellular carrier.

Today’s merger will bring together T-Mobile’s and Sprint’s separate but complementary network assets, combining wide but low-speed T-Mobile low band with mid-range, mid-speed Sprint mid band spectrum and short distance but high-speed T-Mobile high band spectrum. The combined “layer cake” will enable T-Mobile to offer 5G service that switches from fine to good to super-fast based on whatever network assets are locally available, assuming users have devices that can connect to all three types of 5G networks.

For the combined company, the merger critically offers new customer scale and the opportunity for synergies that weren’t available before. The new T-Mobile will now be in the same 100-million-customer ballpark as larger rivals AT&T and Verizon, likely creating additional market pressure with pricing and promotions. On the other hand, T-Mobile is expected to shutter some overlapping Sprint retail locations and has divested some of its network assets and prepaid Boost Mobile customers to Dish Network, which will lead to job changes and some losses — a challenge, given the currently fragile state of the U.S. economy.

Legere’s handoff to Sievert comes a month ahead of the original schedule, which would have seen the famously brash Legere stick around through the end of his contract on April 30. The carrier has promised to maintain the “Un-carrier” spirit and initiatives Legere pioneered as T-Mobile successfully grew from a distant AT&T/Verizon rival to a full-fledged competitor, while “supercharging” them with greater scale.

Federal and state officials delayed the merger multiple times, requiring the carriers to make enforceable service guarantees regarding the scope and speed of coverage. Two major holdout states, New York and California, ultimately decided not to appeal after losing an antitrust lawsuit filed in opposition to the merger.

T-Mobile today said that it will give customers access to “average 5G speeds up to 8 times faster than current LTE in just a few years” and “15 times faster over the next six years,” at which point it will offer 5G to 99% of the U.S. population — with 90% seeing higher than 100Mbps speeds. Additionally, 90% of rural Americans should see average 5G speeds of 50Mbps, faster than current U.S. broadband averages.