SIM Box: How It Works and How You Can Detect It

Dikran Seferian
Dikran SeferianContent Writer

Published: Mar 4, 2024


Cases of telecom fraud have been on the rise over the past few years. At the top of that list is SIM boxing. Many businesses and mobile network operators are suffering from this type of fraud, losing millions of dollars each year. With the increasing reliance on global communication, the telecommunications industry is turning into a playground for fraudulent activities. But on the other hand, the industry is also seeing a lot of technological advancements. And it’s up to network operators to harness those technologies to keep threats—including SIM box fraud—at bay. So what is SIM boxing? Let’s find out. 

What Is a SIM Box?

A SIM box is a device that routes calls through a VoIP (Voice over Internet Protocol) installation. This allows the operator to bypass official gateways and avoid international tariffs. It does so by disguising international calls as local ones.

The device consists of multiple SIM cards from different MNOs, allowing it to work with a number of GSM gateways in various locations. The cards, each with a local number, are connected to the gateway but placed and stored separately. 

How Does a SIM Box Work?

1. Multiple SIM Cards

The first step involves inserting several cards into the SIM box device and assigning a local phone number to each. These can be from the same mobile carrier or different ones. The SIM gateway then uses these cards to make calls. 

2. Configuration

The operator can use specialized software to configure SIM gateways. After installing the cards, they will need to connect the SIM box to the internet through a broadband connection. This allows them to VoIP calls. 

3. International Call Routing

When a phone number controlled by the SIM box operator receives an international call, the SIM box reroutes it via the local cards. Instead of using the official international gateway, the call appears as a local one and incurs lower charges. When a user places an outgoing call, the SIM box intercepts it and chooses a card for the transmission. 

4. Local Number Presentation

Upon receiving a call, the SIM gateway box modifies the caller ID information to show a local number associated with one of the cards. This allows it to hide the international origin of the call. The communication then goes through a local mobile network and appears to come from a legitimate phone number. 

Main Elements of a SIM Box

Hardware Components

  • SIM cards: The SIM cards in the SIM gateway act as a gateway for rerouting international phone calls

  • SIM card slots: The slots that hold the SIM cards determine how many simultaneous calls the SIM box can handle

  • Processing unit: The processing unit is responsible for managing call routing, monitoring call traffic, and presenting international phone calls as local ones

  • Voice transcoding equipment: The voice transcoder adapts call data to the specifications of the local network, converting voice data for transmission

  • Interface to local mobile network: The SIM gateway box links the local network infrastructure to transmit rerouted calls

Software Components

  • Routing algorithm: The routing algorithm determines which SIM card to use for a certain international call, optimizing quality

  • Caller ID spoofing module: The spoofing module manipulates caller ID information to disguise the international origin of the call with a local number from one of the SIM cards

  • Call monitoring and management software: This software keeps track of call traffic, manages the status of SIM cards, and guarantees covert and efficient operation

  • Security features: Operators use security features like encryption and methods of mimicking normal call patterns to avoid detection

What is SIM Box Fraud?

SIM box fraud is a form of the broader interconnect bypass fraud that uses SIM boxes to evade official gateways and international charges by rerouting calls. The main idea behind SIM boxing fraud is to take advantage of the price difference between local and international call rates, allowing the fraud operator to profit by avoiding the higher fees of international calls. Interconnect bypass frauds result in huge financial losses for legitimate telecom businesses. It can also damage the integrity of mobile networks. 

What is The Impact of SIM Box Fraud

1. Poor Quality of Service

By overloading networks with rerouted international phone calls, SIM boxing can degrade the quality of telecom services. The rerouting process leads to call delays, dropped calls, and reduced call quality. This is also because SIM boxing operators often use a cheap and substandard setup. As a result of the poor service quality standards, overloading local networks affects the reputation and customer trust of legitimate telecom businesses. 

2. Global Telecom Fraud Losses

Telecom operators face significant financial losses because of SIM boxing fraud as fraudsters exploit lower rates of local calls, avoiding the higher charges of international phone calls. Besides hindering the profitability of telecom companies, this apparent revenue loss can impede infrastructure investments and can even lead to higher service costs for legitimate users. SIM boxing scams escape government taxes and surcharges as well, obstructing revenues that fund infrastructure, welfare schemes, and other state projects. 

3. Threat to National Security

As SIM boxing frauds enable unauthorized interception of international phone calls, they pose a serious threat to national security. Criminal entities can carry out illegal activities through SIM boxes by exploiting unmonitored communication channels. These activities can include smuggling, terrorism, and other forms of organized crime. National security agencies will ultimately find it very challenging to track criminal activities through communication networks. 

4. Damage to Infrastructure

The increasing use of SIM box gateways can damage the telecom infrastructure by overloading local networks and causing congestion. In some cases, it can even lead to system failure. The overload can result in hardware wear and tear in addition to higher maintenance costs and the need for infrastructure upgrades. In turn, this can disrupt the smooth operation of communication networks and impede technological advancements. 

5. Compromised Privacy and Security

By manipulating caller ID information and rerouting calls through unauthorized channels, SIM boxing fraud puts the privacy and security of individuals at risk. The compromised integrity of the telecom network opens the way for security breaches like eavesdropping and unauthorized access to confidential information. This not only violates the privacy rights of users but also poses threats to governmental communications, sabotaging the overall security of the telecom industry. 

How to Detect SIM Boxes

Analyze Call Patterns

Analyzing call patterns is where you scrutinize the timing, frequency, and duration of phone calls to pinpoint irregularities. SIM box operators usually display abnormal behavior, like high call volumes during off-peak hours or an unusual concentration of calls to certain destinations. With strong call pattern analysis tools, telecom operators can detect suspicious activities and investigate potential SIM boxing operations based on deviations from normal patterns.

Examine Geographic Anomalies

Keeping an eye out for geographic anomalies in call traffic is key for detecting SIM box fraud. By masking international calls as local ones, SIM gateway boxing causes unusual patterns in call distribution.

Different mobile operators must closely monitor the geographic origins and destinations of calls. Identifying anomalies helps to pinpoint the possibility of SIM boxing and take the necessary steps to stop the fraud in its tracks and prevent the significant security threat it poses.  

Do Randomized Testing

Carry out randomized testing by making test calls to different destinations to evaluate the integrity of the network. This proactive approach allows telecom operators to reveal potential SIM VoIP gateway fraud by examining deviations in call routing and quality. Regular yet unpredictable testing helps to stay ahead of fraudsters who often adjust their activities when they anticipate routine monitoring. This enables faster detection of compromised security and response to emerging risks. 

Track International Gateway Traffic

Another way to detect SIM boxing is by keeping track of international gateway traffic. Legitimate international calls are supposed to pass through official gateways and any deviation from that can be a red flag. By closely monitoring the traffic at international gateways, telecom operators can identify calls that are bypassing official channels. Such calls can point toward SIM boxing and require further investigation.

Assess Voice Quality

Since rerouted calls often experience degradation, you can detect SIM box frauds by analyzing voice quality parameters. Anomalies like call drops, call delays, and poor audio quality can indicate the rerouting of calls via unauthorized channels. By keeping a close eye on voice quality and addressing any deterioration on the spot, telecom operators can pinpoint SIM boxing and take measures to mitigate it.

How to Prevent SIM Box Fraud

Geographic Filtering

Geographic filtering involves taking measures to block calls with suspicious geographic anomalies. By analyzing call metadata and patterns, MNOs can place filters that detect and limit deviations from normal calling behavior based on the call’s origin and destination. The geographic filters act as a proactive defense mechanism, making sure calls follow normal geographic patterns and contributing to the security of the telecom network.

Secure SIM Card Management

Secure SIM card management is the act of applying solid practices for the storage, distribution, and activation of SIM cards. By safeguarding the whole lifecycle of SIM cards from production to delivery, mobile network operators can reduce the risk of unauthorized access and tampering.

This prevention method helps to protect against SIM gateway operators who take advantage of weak spots in the ecosystem. Ultimately, it contributes to a more secure and resilient telecom infrastructure. 

International Collaboration

A good strategy for combating SIM gateway fraud—which often involves cross-border activities—is international collaboration. By building partnerships with international carriers, telecom regulatory bodies, and law enforcement agencies, mobile operators can share intelligence and information.

Collaborative efforts allow for a coordinated response to the evolving nature of SIM boxing fraud, guaranteeing a more effective approach to prevention. Exchanging insights on common fraud schemes and emerging threats boosts the collective ability to identify and block fraud on a global scale.

Get in Touch With Our Experts

Streamline your efforts and centralize your channels with Dexatel's all-in-one platform. Talk to our experts and get all your questions answered.

Network Security Systems and Dexatel NPT

Network security systems, like Dexatel’s Network Penetration Testing (NPT), play a major role in preventing SIM box fraud by protecting the network’s integrity. Alternatively known as Network Protection Technology, NPT solutions leverage advanced technologies like firewalls, privacy and security encryptions, as well as intrusion detection systems to control network traffic. 

Dexatel’s NPT tool detects and blocks a variety of IP bypasses, including P2P, voice channel, and local interconnects bypasses. Users benefit from versatile A2P testing, multi-device optimization, and global language integration. The testing tool also offers real-world simulations with multiple SIMs. 

NPT solutions can identify and prevent potential threats by SIM boxing operators. Taking such strong network security measures mitigates weaknesses and creates a safe environment for legitimate communication services.