TracFone Wireless Inc., owned by America Movil S.A.B. de C.V., has agreed to pay $40 million to reimburse customers who purchased prepaid unlimited data plans that turned out to have maximum limits, the Federal Trade Commission said Wednesday. The FTC alleged that TracFone advertised unlimited data plans for $45 a month but either cut off or slowed, or "throttled," the data once a fixed limit was hit.