Abstract: As mobile devices grow in popularity and ubiquity in everyday life, they are often involved in digital crimes and digital investigation as well. Cell phones, for instance, are becoming a media or tool in criminal cases and corporate investigation. Cellular phone forensics is therefore important for law enforcement and private investigators. Cell phone forensics aims at acquiring and analyzing data in the cellular phone, which is similar to computer forensics. However, the forensic tools for cell phones are quite different from those for personal computers. This paper briefly explains the basics of the GSM system. Evidence items that can be obtained from the Mobile Equipment, the SIM and the core network are explored. Tools to extract such evidence from the components of the system exist, but there is a need to develop more sound forensic procedures and tools for extracting such evidence.