Nervous System: Who Ya Gonna Call—and Who's Calling You?

Creating what would become CallerID meant overcoming three challenges: the basic technical challenge of establishing a process to signal the origin of a call; the logistical challenge in deploying that technical solution across networks; and persuading a skeptical public that this technology was not a grievous privacy violation.

Early telephony connected people who already knew each other through an intermediary who likely knew them both. That changed as telephone networks grew and brought tension between the needs for privacy versus screening one’s calls. Call screening would require transmitting to the receiver the identification of the originating call—that is, “Caller ID.” Making this work over a network that was never designed for such a thing would take creativity.

Essentially, implementing a method of caller identification meant overcoming three challenges: the basic technical challenge of establishing a process to signal the origin of a call; the logistical challenge in deploying that technical solution across networks; and perhaps thorniest of all, persuading a skeptical public that this technology was not a grievous privacy violation.

The first baby steps toward solving these puzzles came in 1967 when AT&T Bell Labs engineer Amos E. Joel Jr. proposed that telephone companies should develop a means to identify the origin of an incoming call to help the recipient decide whether to answer the phone. Joel was a specialist in electronic switching systems, and many of his core technologies remain in use today throughout the telecommunications industry. But despite his solid chops as a pioneer of foundational telecommunications technology, his thoughts about a caller identification service were entirely theoretical. No such technology then existed, nor did he propose any ideas.

Nevertheless, telephone companies recognized the inherent value in such a system—and looked forward to charging subscribers a special fee for the service. In many ways, this incentive solved the logistical problem before the technology even existed. If a technical solution could be found, the profit motive would ensure that the carriers implemented it.

This is where engineer Theodore George Paraskevakos comes into the story. Beginning in 1968, Paraskevakos began developing a method to encode the network address of the originating telephone (that is, its area code and telephone number) as electronic pulses. This was not hugely different from the existing methods of using encoded pulses to signal the destination address. Paraskevakos filed for his patent in 1971. The technology matured somewhat between 1971 and its eventual deployment, but the key principles were in place.

The method works by transmitting the caller identification data within the same audio channel used for the voice communication itself, a technique called “in-band signaling.” During the gap between the first and second rings of an incoming call, a machine-readable “dual-tone multi-frequency” (DTMF) signal alerts the receiving telephone to mute its speaker, which ensures that the call recipient does not hear any intrusive sound if they answer the call before the signaling process is completed. The transmitting telephone then transmits pulses representing the originating calling number and a date/time reference and signals the receiving device to unmute the speaker.

Exactly how to best represent that caller identification signal, though, was a separate question. Despite initial consideration of having an operator speak the information aloud, it was deemed more efficient to develop a device to display the incoming telephone number.

In 1976, developer Kazuo Hashimoto designed a prototype device that could visually display the decoded pulses on a screen. Although developed as a standalone box, the display was later incorporated into the telephone’s design.

AT&T announced the system in 1978 under the brand name “Caller Identification Service” or CIDS. Interested users paid a separate subscription fee and needed specially designed phones that incorporated the decoding and display technologies.

This service, eventually renamed CallerID, first became available for consumer use in a 1984 test rollout in Orlando, Florida. Over the rest of the 1980s, the service began to spread to homes in other areas as well. In 1986, the FCC mandated that all telecom providers provide CallerID services so that users would not be denied access to the technology based on their network provider.

This moment surfaced the aforementioned third challenge. Just as the FCC was mandating nationwide access to the service, several states were passing laws requiring that telecom providers allow users to block that very service.

Consumers were accustomed to making calls anonymously. The notion that tech companies could simply expose their telephone numbers felt like an unprecedented privacy violation to many people.

The public pushback was intense enough that carriers implemented Caller ID Blocking to allow users to block their numbers from being displayed, either permanently or on an ad-hoc basis by pressing *67.

Decades of subsequent experience with CallerID softened that public anxiety. Indeed, contemporary telecommunications regulations such as “Secure Telephone Identity Revisited” (STIR) and “Signature-based Handling of Asserted information using toKENs” (SHAKEN) take for granted that CallerID is a bulwark against spam calls and stipulate that auditable caller identification services function over modern communications networks. Ironically, what was once perceived as a risk to consumer privacy has come to be embraced as a consumer privacy protection tool.

The views and opinions expressed in this article are those of the author and do not necessarily reflect the opinions, position, or policy of Berkeley Research Group, LLC or its other employees and affiliates.