If anyone else is curious about this, it appears there are two relevant cases: - Hush-a-Phone Corp v., United States[0], in which the DC Circuit Court of Appea

If anyone else is curious about this, it appears there are two relevant cases: - Hush-a-Phone Corp v., United States[0], in which the DC Circuit Court of Appeals ruled that AT&T could not prohibit the mechanical attachment of a device to its phones as long as the device did not damage AT&T's phone or its network - The Carterfone decision[1], where the FCC allowed third-party devices to be electrically connected to AT&T's network as long as they did not damage the network [0]: https://en.wikipedia.org/wiki/Hush-A-Phone_Corp._v._United_States https://en.wikipedia.org/wiki/Hush-A-Phone_Corp._v._United_S... [1]: https://en.wikipedia.org/wiki/Carterfone https://en.wikipedia.org/wiki/Carterfone