This study investigated the correlation between product line extension and customer loyalty among GSM companies in Rivers State. The study aimed to examine the correlation between horizontal extension, vertical extension, and customer loyalty. It also determines how technology influences the relationship between product line extension and customer loyalty. Seven (7) hypotheses were developed and evaluated in their null versions. The study employed a survey research methodology. The primary data was gathered from 367 respondents, representing the whole customer base of the four registered GSM Companies in Rivers State, utilizing structured questionnaires. The gathered data were examined utilizing percentages, Pearson Product Moment Correlation, and partial Correlation through SPSS. The investigation dismissed all seven null hypotheses, hence supporting the alternative hypothesis. A substantial and significant association was identified between product line expansion and its dimensions of horizontal and vertical extensions, as measured by customer loyalty indicators such as referrals, price insensitivity, and repeat purchases in GSM companies. The outcome also indicated that the contextual variable—technology—substantially influences the link between product line extension and customer loyalty. The study determined that the expansion of product lines influences consumer loyalty within GSM companies. It was suggested that GSM companies improve their customer service by adding more network facilities to make the best use of GSM technology. It was suggested that the Nigerian car industry look into product line extension and effectiveness in order to improve the quality of our local manufacturing.