This study deals with a call control strategy in a dual-mode time-division multiple access (TDMA) cellular system, which provides services both to analog and digital calls. Since analog calls consume the frequency resource several times as much as digital calls, we consider a call control strategy of the threshold type that the number of active analog calls is restricted within a prespecified level, Given the arrival rates and the GOS's for both types of calls in the cells, two nonlinear integer optimization problems are considered for a multicell system as well as for a single cell system, The one is to find the threshold parameters optimizing the relevant objective measures. The other is to obtain the minimum numbers of required channels in the cells satisfying the GOS's of both types of calls. The solution methods for the two kinds of optimization problems are devised based on the interesting properties of the objective function and the blocking probabilities of both call types. And the efficiency of the proposed algorithms is verified by extensive computational experiments with realistic input data.