Telephone spam has been among the highest network security concerns for users for many years. In response, industry and government have deployed new technologies and regulations to curb the problem, and academic and industry researchers have provided methods and measurements to characterize robocalls. Have these efforts borne fruit? Are the research characterizations reliable, and have the prevention and deterrence mechanisms succeeded? In this paper, we address these questions through analysis of data from several independently-operated vantage points, ranging from industry and academic voice honeypots to public enforcement and consumer complaints, some with over 5 years of historic data. We first describe how we address the non-trivial methodological challenges of comparing disparate data sources, including comparing audio and transcripts from about 3 million voice calls. We also detail the substantial coherency of these diverse perspectives, which dramatically strengthens the evidence for the conclusions we draw about robocall characterization and mitigation while highlighting advantages of each approach. Among our many findings, we find that unsolicited calls are in slow decline, though complaints and call volumes remain high. We also find that robocallers have managed to adapt to STIR/SHAKEN, a mandatory call authentication scheme. In total, our findings highlight the most promising directions for future efforts to characterize and stop telephone spam.

The United States government has begun to take significant steps to eliminate robocalls. The FCC requires that phone companies use a cryptography-based technology called STIR/SHAKEN to authenticate all callers' IDs beginning June 30, 2021. Anyone hoping for robocalls to evaporate in a puff of regulation will be sorely disappointed. However, respite may be on the way, albeit slowly. The technology to block robocalls is developing, and STIR/SHAKEN is part of a trend in which phone consumers in the United States are no longer solely responsible for deciding whether or not to accept robocalls.