If anyone else wants to know the significance of this device, it allowed for the argument to be made that any device should be able to be connected to the network, provided it did not interfere with it. It paved the way for non-AT&T equipment. The FAX and answering machines were allowed as a result (many people/industries still cling to these ideas; they are the reason voicemail hasn't gone the way of the dinosaur). Skype used it in '07 to

"petition for rulemaking was filed with the FCC by Skype, requesting the FCC to apply the Carterfone regulations to the wireless industry—which would mean that OEMs, portals and others will be able to offer wireless devices and services without the cellular operators needing to approve the handsets. However, on 1 April 2008, FCC chairman Kevin Martin indicated that he would oppose Skype's request.[3]"

I was about to post this and say that the parent comment does not remember this because it happened 4 years before their birth.

Tbh, it happened a number of years before my birth as well, but some of us choose to learn the history of computation / networking. ;-)

The Carterfone was an early exception because of its functionality.