The FCC has opened a comment docket on the proposed T-Mobile-Sprint merger and signaled the deal is about to be filed with the commission.

The two wireless companies announced Sunday (April 29) that they had struck a deal to merge that valued the combined company at $146 billion (including debt).

Related: D.C. Eyes T-Mobile-Sprint Merger

It is only the latest in a flurry of merger activity, from the approval of the AT&T-Time Warner deal by a federal judge to Comcast's announced play for 21st Century Fox assets.

Related: Computer Companies Seek Thorough Review of T-Mobile-Sprint Deal

The FCC has even set up its 180-day shot clock on the proposed T-Mobile-Sprint meld, though it will be on day zero until after the deal is filed, which could come today (June 18).

If approved, Deutsche Telekom would be the largest single shareholder in the combined company, which would merge the number three and number four carriers in the U.S., which the companies argue would provide a stronger competitor to the Big Two, Verizon and AT&T, rather than anticompetitively reducing the number of major players from four to three.

The Senate Judiciary Committee's Antitrust Subcommittee plans to hold a hearing on the deal June 27.

Some Senate Democrats have told the Department of Justice and the FCC that they have serious concerns about the merger.

They want both agencies to ponder "(1) the impact of reducing the number of national wireless carriers from four to three; (2) how the proposed merger would affect lower-cost options for wireless service; (3) whether specific regions, particularly rural areas, would be disproportionately affected by the proposed transaction; and (4) the proposed transaction’s likely effect on innovation of wireless networks and other technologies."

Sprint and T-Mobile's top execs argue that the merger would create a maverick carrier with the scale to take on AT&T and Verizon--and Comcast and Charter--and would be the best positioned to help the U.S. lead in 5G.

The execs have suggested it is no longer the Big Four--AT&T, Verizon, T-Mobile and Sprint--but the Big Seven or Eight, including the cable ops getting in on the wireless action.