In next-generation wireless networks, OFDM is a potential key technology. Subcarriers in the OFDMA networks are scarce and valuable, operators should manage them efficiently by radio-resource management function. Several OFDMA subcarrier-allocation schemes and performance-evaluation methods have been widely studied, but very few studies focused on managing call blocking probability (CBP) and bandwidth utilization (BU). CBP and BU are two important performance measures, which respectively represent the quality of service for subscribers and the profit of operators. This paper proposes an evaluation model to accurately predict the subcarrier-allocation performance, especially in consideration of the CBP and BU. Theoretical and simulation results indicate that the model works. In addition, the CBP and BU are adopted to solve a subcarrier utilization-optimization problem, which can be applied in network planning and re-planning processes. The optimization problem uses given traffic load and specified maximum CBP constraint to maximize the BU by discovering the optimal number of subcarriers in a base station. Finally, operators may utilize the results to manage their subcarriers flexibly, and to improve their profitability.