On May 3 2012, the Competition Appeal Tribunal (CAT), the UK appeals court for competition matters, upheld Ofcom’s decision to move from an average cost to a marginal cost measure for the way that interconnection rates between mobile networks are computed. In Europe, mobile operators pay regulated wholesale interconnection rates to other networks for terminating cross-network calls. Philip Kalmus of Compass Lexecon’s London office acted as the expert for mobile operator “Three,” an intervener on behalf of Ofcom. Kalmus’ economic reasoning, set forward at the hearing, was accepted by the Competition Commission, acting as advisors to the CAT, over the arguments of opposing experts from three other firms. During the course of the proceedings, Compass Lexecon took on a larger role, replacing another firm that had acted as a joint advisor. Kalmus was assisted by Bertram Neurohr, Stefano Trento, and Scott Holbrook in our London office.