The smartphone market is very price sensitive due to high commercial competitiveness and constant technological evolution. Price elasticity and cross-elasticity are critical for adjusting sales forecasts to avoid disruptions and / or high inventory volumes. This work presents a modeling proposal for calculation of price elasticity and cross elasticity using causal variables, addressing the internal and external aspects of a telecommunications service operator with several own stores. The variable s choice is the result of a partnership between professionals in Logistics, Marketing and Sales providing technical support to Demand Planners. In order to calculate price elasticity, modeling based on dynamic regression indicated the use of variables: internal competitors prices (typifying cannibalization), availability (for launching and phase-out of products), open store (differentiating from the days of closed stores with zero sales) and daily factor (daily sales rhythm), providing satisfactory results and demonstrating commercial applicability of the proposed model.