The purpose of this study is to understand the mobile carrier choice behavior considering the current market in Japan. The mobile phone market in Japan was mainly shared by three Major Mobile-Carriers (3MMC): docomo, au, and SoftBank. However, the number of Mobile Virtual Network Operators (MVNOs) customers has been increasing recently, and Rakuten Mobile has entered the mobile phone market as a Mobile Network Operator (MNO) since 2020. Under such competitive conditions, MNOs and MVNOs need an appropriate method to develop service strategies to increase their market share. To understand users' mobile carrier choice behavior, we analyzed the differences between users who intend to continue with their current mobile carrier and those who intend to change to another mobile carrier on the basis of IT service management platform that we proposed. In addition, we demonstrated useful information for service strategies to prevent users from changing to other mobile-carriers.