The study is conducted on quality of service delivery and its effect on customer satisfaction in the case of Ethiotelecom in Oromia region in Ambo area on mobile telephone users. This study tried to provide relevant factors that cause customers to respond about mobile phone services delivered by Ethio-telecom. The research approach employed for the study is mixed approach i.e. both qualitative and quantitative approached used to find out the effect of Ethio-telecom service quality on customer satisfaction. For the purpose of the study both primary and secondary data are used. The primary data are collected through questionnaire and interview with the Ambo branch Ethio-telecom employees, manager and customers. Furthermore, secondary data are taken from documents and brochures that are available from the branch office. The research design employed is descriptive and uses charts and frequency table to discuss the output. A sample of 500 were selected through simple random sampling from the total population. Result of the study shows that mobile phone users faces awe-inspiring number of the problems like network busy, error in connection, poor network coverage, slow mobile internet service and expensive price of the service.