Competition in some telecommunication services has emerged in Japan since deregulation of telecommunication markets in 1985. Demand forecasting methods which take into account competition and investment plan based on it should be studied. There are many forecasting and network planning methods, but most of them do not take into account competition. Thus, in this paper, the competitive Bass model, attraction model, regression model and entropy model are discussed as forecasting methods which can be used under competitive environment. Most of the existing planning methods have treated costs and interest rates as deterministic values, but in fact they are not deterministic. Thus, we show a method which represents undefined factors by fuzzy numbers with triangular membership functions.