Bad Actors Exploit Non-IP Networks of Smaller Carriers in Growing Robocall Threats, Reveals TNS 2025 Half-Year Report
New findings from the Transaction Network Services (TNS) 2025 Half-Year Robocall Investigation Report reveal a concerning trend: bad actors are increasingly exploiting vulnerabilities in smaller carrier networks that have yet to fully transition from legacy systems to all-IP networks. The report highlights how tactics like SIM boxing and other evolving methods are being used to infiltrate non-IP traffic, enabling fraudsters to launch widespread robocall campaigns.
The data underscores the stark contrast between tier-1 carriers and their smaller counterparts. In the first half of 2025, 84% of call traffic between top U.S. telecom providers—Verizon, UScellular, T-Mobile, Lumen, Comcast, Charter, and AT&T—was signed and verified using STIR/SHAKEN protocols. This demonstrates that tier-1 operators are maintaining high success rates in protecting their subscribers from unwanted robocalls. However, only 21% of calls originating from non-tier-1 carriers were signed, leaving significant gaps for exploitation.
“Tier-1 operators have achieved consistently high levels of signed call traffic thanks to their migration to SIP networks and implementation of STIR/SHAKEN,” said Seth Walton, TNS’ General Manager of Communications Market. “But our report underscores a critical issue: until more smaller carriers complete their migration to SIP-to-SIP connectivity, bad actors will continue to find pathways to launch robocall campaigns. Regulators, policymakers, and industry leaders must prioritize cost-effective technologies and strategies to accelerate this transition.”
Challenges Facing Tier-1 Operators and Smaller Carriers
While tier-1 operators boast impressive metrics—94% of call traffic between them was signed with “A-level” attestation—challenges persist. A-level attestation indicates that these operators have established secure SIP-to-SIP connections between originating and terminating parties, making it harder for robocallers to infiltrate their networks. However, authentication issues are emerging as invalid attestation becomes more frequent. Spam calls are slipping through with improperly signed A-level attestations, highlighting the need for additional verification measures to close loopholes exploited by bad actors.
Smaller carriers face even greater hurdles. Although those capable of signing calls maintained strong attestation levels (93% of signed traffic included A-level attestation), many smaller carriers are still struggling to migrate fully to IP networks. This delay has created opportunities for fraudsters to hide unwanted call traffic. In response, the Federal Communications Commission (FCC) adopted a Notice of Proposed Rulemaking aimed at mandating and facilitating stronger call authentication frameworks for non-IP networks.
Top Robocall Scams of 2025
The report also sheds light on the most prevalent robocall scams during the first half of the year. One of the most insidious schemes involved IRS impersonation, where fraudsters spoofed legitimate IRS numbers to demand payment for alleged back taxes. Victims were threatened with arrest or imprisonment if they failed to comply, preying on fear and confusion.
Another alarming development is the rise of SIM boxing, also known as interconnect bypass fraud. Historically associated with exploiting price disparities between local and international call rates, SIM boxing has evolved into a tool for launching robocall spam campaigns. Fraudsters use multiple SIM cards to conceal malicious traffic within trusted networks, making it difficult for operators to detect and tag these calls. Because the traffic appears to originate from within the network, it often evades scrutiny.
Other common scams include fund recovery schemes, Google Voice phishing attempts, solar power promotions, and precious metal investment pitches. These scams target unsuspecting consumers with deceptive promises or threats, further underscoring the need for robust anti-robocall measures.
Americans Take Action Against Robocalls
Encouragingly, Americans are becoming more proactive in reporting robocall activity. According to recent TNS survey data, 43% of respondents filed a complaint about robocalls with their state’s Attorney General, the Federal Trade Commission (FTC), or the Do Not Call Registry in the past 12 months. This marks a significant increase from 2023, when only 28% reported such incidents. This growing awareness reflects public frustration with robocalls and a desire for stronger enforcement mechanisms.
A Call to Action for the Industry
The TNS 2025 Half-Year Robocall Investigation Report serves as both a progress update and a wake-up call. While tier-1 carriers have made commendable strides in combating robocalls, the persistence of vulnerabilities among smaller carriers highlights the urgent need for industry-wide collaboration. Policymakers and regulators must work together to provide financial and technological support to smaller carriers, enabling them to complete their transitions to IP networks. Additionally, advancements in call verification technologies and stricter enforcement of existing regulations can help close the gaps exploited by bad actors.
As robocall tactics grow more sophisticated, so too must the tools and strategies used to combat them. By addressing the challenges faced by smaller carriers and fostering a unified approach across the telecom industry, stakeholders can build a safer, more secure communications environment for all users.
About TNS:
TNS, a market leader in call analytics and robocall mitigation, provides an end-to-end ecosystem for protecting, and restoring trust in, voice calls. TNS addresses the full needs of wireless and wireline operators globally with TNS Call Guardian® the industry-leading call analytics solution that protects subscribers from high risk and nuisance robocalls. In addition, its Enterprise Branded Calling solution is the core component of its Identity Analytics Suite that is taking the next step in enriching consumer engagement, making voice calling an integral part of an omnichannel customer experience program. TNS analyzes over one billion call events across more than 500 operators every single day, enabling carriers to identify more unwanted robocalls.
