In this paper, we study on the price comparison between shared plan and non-shared plan for mobile service. A non-shared data plan is a traditional data plan for a single user with a limited monthly data allowance. A shared data plan allows a user to add different devices to one inclusive plan and receive one bill at the end of every month, which the monthly data allowance is shared by a group of users across multiple devices. Each data plan is charged by a fixed price for a monthly data allowance and there will be an extra charge if a user consumes more than the monthly data allowance. Therefore, the charged price is affected by the user's behaviors. We study the users' behaviors by observing the measured data from Chunghwa Telecom and derive stochastic models for shared plan and non-shared plan to evaluate monthly prices based on different users' behaviors. We recommend the most appropriate plan for a group of users based on users' behaviors. On the other hand, mobile operators can attract more customers and earn more profit. We show that the shared plan is a 'win-win' plan for users and operators.