UNITED STATES COURT OF APPEALS FOR THE SIXTH CIRCUIT

┐ BRANDENBURG TELEPHONE COMPANY, │ Plaintiff-Appellant, │ > No. 23-5369 │ v. │ │ SPRINT COMMUNICATIONS COMPANY L.P., │ Defendant-Appellee. │ ┘ Appeal from the United States District Court for the Western District of Kentucky at Louisville. No. 3:09-cv-00109—Claria Horn Boom, District Judge.

Decided and Filed: January 10, 2024

Before: SUTTON, Chief Judge; STRANCH and MATHIS, Circuit Judges. _________________

COUNSEL ARGUED: Edward T. Depp, DINSMORE & SHOHL, Louisville, Kentucky, for Appellant. Philip D. Williamson, TAFT STETTINIUS & HOLLISTER LLP, Cincinnati, Ohio, for Appellee. ON BRIEF: Edward T. Depp, John E. Selent, R. Brooks Herrick, Anne Stewart Myers, DINSMORE & SHOHL, Louisville, Kentucky, for Appellant. Philip D. Williamson, Annie M. McClellan, TAFT STETTINIUS & HOLLISTER LLP, Cincinnati, Ohio, Philip R. Schenkenberg, TAFT STETTINIUS & HOLLISTER LLP, Minneapolis, Minnesota, for Appellee. _________________

OPINION _________________

SUTTON, Chief Judge. After more than a decade of regulatory and judicial proceedings, Sprint Communications concedes that it failed to pay Brandenburg Telephone Company in full for connecting local telephone calls and now owes $2.2 million plus compound interest. This appeal concerns one residual question: the interest rate on the award. Sprint says that No. 23-5369 Brandenburg Telephone Co. v. Sprint Comm’ns Co. L.P. Page 2

Brandenburg’s filed utility tariff sets the interest rate at 8%, and that Sprint is on the hook for $4.3 million in interest. Brandenburg replies that the tariff imposes a rate of 10.66%, bringing Sprint’s bill to $7.1 million in interest. The district court ruled for Sprint. We affirm.

I.

Brandenburg provides local telephone services in central Kentucky. In view of the monopolistic nature of this utility service, it is heavily regulated. State and federal law require Brandenburg to obtain regulatory approval for the terms and conditions of its services. Once a regulator approves the filed tariff, anyone who uses the service must abide by the rates. See generally Am. Tel. & Tel. Co. v. Cent. Off. Tel., Inc., 524 U.S. 214, 221–23 (1998). Brandenburg has one tariff with the Kentucky Public Service Commission for calls that begin and end in Kentucky and another with the Federal Communications Commission for interstate calls.

Among other services, the tariffs cover switched access services, which allow long- distance providers such as Sprint to connect calls to local numbers. At the time relevant to this appeal, the Kentucky tariff set a higher charge for this service than the federal tariff did. Brandenburg determined which calls were intrastate by comparing their area codes. That approach may have worked in the past. But Sprint claimed that the approach inflated the intrastate rates because cellphones use the same area code no matter where the call originates. When Brandenburg declined to change its billing method to account for this possibility, Sprint began withholding pa