Provided are methods and systems for detecting and preventing bypass fraud in telecommunication networks, primarily for detecting and preventing SIM box fraud in telecommunication networks. The methods include generating one or more test calls from a remote agent to a local agent where the remote agent can be a roaming agent or a remote dialer. The local agent is a subscriber number. The methods further include facilitating call forwarding of the test calls from the local agent to a local number. The methods include identifying the presence of bypass fraud by analyzing caller identification information of the test call received on the local number. Finally, the methods include preventing future use of a detected SIM box.