This study aims to present opportunities and challenges for phone retailers in particular and commercial and service businesses in general. The closure of Vien Thong A is an expensive lesson for businesses that follow. The thesis has introduced the basic issues of CRM, how Vien Thong A applies CRM to sales activities in its store chain. Moreover, the thesis also synthesizes several different newspapers related to the CRM service of competitors to collect data, compare and analyze the advantages and disadvantages of Vien Thong A with its competitors. The research results show that some concepts of customers are generalized according to classical and modern concepts, and at the same time, the author's concept of customers is introduced, including classifying customers according to some basic criteria, customer value and satisfying customer's expected value. These are basic and practical issues related to CRM and are the basis for research.