Anyone can file petitions to deny, and you might expect to see some from consumer advocacy groups and industry experts who may be concerned over the reduction in the number of national carriers from four to three. The FCC has laid out a 180-day review timeline to determine whether the merger is in the public interest, but that's more of a guideline and there's no required deadline for the agency to issue a decision.

While the Trump version of the FCC is generally more business-friendly than the previous incarnation, there's no guarantee the agency will rubberstamp the T-Mobile and Sprint tie-up. Just this week, the FCC effectively ended Sinclair's chance of merging with Tribune Media over concerns about TV station ownership.