Updated at 3:07 p.m. ET T-Mobile and Sprint have reached a "definitive agreement" to merge in an all-stock deal, which would create a new company with a total value of $146 billion, based on current stock prices. The two companies — the third- and fourth-largest U.S. wireless carriers, respectively, behind Verizon and AT&T — have been trying to merge for years. But previous efforts have failed, often falling apart under intense regulatory scrutiny. This deal still needs regulatory approval, from both the Justice Department, which will weigh antitrust concerns, and the Federal Communications Commission, which will consider whether the deal is in the public interest. U.S. regulators have recently challenged AT&T's $85 billion deal to purchase Time Warner Inc., Reuters notes, and "are expected to grill Sprint and T-Mobile on how they will price their combined wireless offerings." The companies say merging will allow them to lower prices and put more pressure on Verizon and AT&T.