This study examines the effects of handset subsidy regulation on mobile carriers’ profits, consumer surplus, and social welfare. I consider three cases of regulating handset subsidies. The first case is when excess subsidies are permitted. The second case is when the subsidy cap is set. The third case is when the subsidy regulation is abolished. Considering two carriers competing in subsidies in existing and new markets, I show that the carriers’ profits are highest in the first case. If competition in a new market is sufficiently intense and the subsidy cap is sufficiently high, then consumer surplus is highest in the second case. Otherwise, it is highest in the third case. Social welfare is highest in the second case. The results suggest that from the viewpoint of social welfare, setting a subsidy cap may be effective. If the objective of policy is to increase consumer surplus, the regulatory agency needs to consider the level of competition in a new market and the subsidy cap.