57 commercial mobile service or the functional equivalent of a commercial mobile service, as specified by regulation by the Commission.” Id. § 332(d)(3). Because private mobile service is a residual category defined in relation to commercial mobile service, the definition of commercial mobile service is the operative one for our purposes. There is no dispute that mobile broadband meets three of the four parts of the statutory definition of commercial mobile service. Mobile broadband is a “mobile service”; it “is provided for profit”; and it is available “to the public” or “a substantial portion of the public.” Id. § 332(d)(1). In those respects, mobile broadband bears the hallmarks of a commercial—and hence not a private—mobile service. The sole remaining question is whether mobile broadband also “makes interconnected service available.” Id. The statute defines “interconnected service” as “service that is interconnected with the public switched network (as such terms are defined by regulation by the Commission).” Id. § 332(d)(2). Until the Order, the Commission in turn defined the “public switched network” as a set of telephone (cellular and landline) networks, with users’ ten-digit telephone numbers making up the interconnected endpoints of the network. Specifically, “public switched network” meant “[a]ny common carrier switched network . . . that use[s] the North American Numbering Plan in connection with the provision of switched services.” 47 C.F.R. § 20.3 (prior version effective through June 11, 2015). The “North American Numbering Plan” (NANP) is the ten-digit telephone numbering plan used in the United States. See In re Implementation of Sections 3(n) & 332 of the Communications Act (“1994 Order”), 9 FCC Rcd. 1411, 1437 ¶ 60 n.116 (1994).