In today’s world, data mining has increasingly become very interesting and popular in terms of all application. Telecommunication companies generate a tremendous amount of data. These data include call detail data, which describes the calls that traverse the telecommunication networks. Data is a very important ingredient and extracting knowledge from the data serves great purposes to the users.This work helps in identifying the activities Segmentation of mobile customers of different groups will be done based on some rules. The basic principles of data mining are to analyze the data from the different angle, categorize it and finally to summarize it. The need for data mining is that we have too much data, too much technology but don’t have useful information. Data mining software allows the user to analyze data. This paper introduces the key principle of data pre-processing, Segmentation, classification, clustering and introduction of WEKA tool.Weka is a data mining tool. It provides the facility to classify the data through various algorithms. Data mining is the process of analyzing data from different viewpoints and summarizing it into useful information. Data mining is one of the top research areas in recent days. WEKA is a data mining tool, it provides the facility to classify and cluster the data through machine learning algorithm.