Mobile phone data has become a crucial resource in mobility studies, offering a rich dataset for analysing human movement. This paper provides a comprehensive review of mobile phone data sources and their applications in transportation research. It examines the strengths and limitations of various data types, including Call Detail Records (CDR), cellular signalling data (CSD), and synthetic CDR. The study highlights methodologies for travel demand estimation, origin-destination (OD) matrix generation, and mode-specific OD estimation. While CDR data has demonstrated reliability in trip purpose estimation, challenges remain in accurately predicting travel modes. The paper concludes with recommendations for improving synthetic CDR data and broadening its applications in mobility studies.