Knowledge management system infrastructure is at the forefront of knowledge management practice. Knowledge must be identified, captured, and shared to improve KM practices; however, little is known about the successful implementation of KMS infrastructure by Namibian mobile telecommunications companies. This mixed-methods research study employed a convergent parallel design and parallel sampling techniques. Three hundred and nine online questionnaires were distributed to a representative sample, with a response rate of 57%. Computer software packages were used to analyse quantitative data quantitatively, and qualitative data from interviews with 11 participants and analysis of documents were analysed thematically. Findings showed that infrastructure, management support, and employee participation were necessary for a successful KMS infrastructure implementation for effective and efficient KM practices. The study provides MT companies with a foundational understanding of how the infrastructure for KMS is essential for effective and efficient KM practice.