I am curious to know if US landline carriers have safe harbor for carrying illegal calls? That is, are the carriers somehow immune from an action when they carry illegal calls on their network?
The changing tide and specific details are (1) carriers are accepting and completing calls from known robocallers and other miscreants, and (2) the FTC's 2017 ruling that carriers can block the traffic at the network level.
The insight for (1) is, carriers have available lists of some robocallers and other miscreants. Two lists are (a) the FTC Do Not Call data files, and (b) reports of harassing calls from some robocallers and other miscreants via Unlawful Call Centers (i.e., *57).
The change for (2) is from the FTC. It is Advanced Methods to Target and Eliminate Unlawful Robocalls, CG Docket No. 17-59, published in FCC-CIRC1703-01. Specifically (D)(8) states:
To aid the Strike Force and other providers’ call blocking efforts, the Consumer and Governmental Affairs Bureau (Bureau) released a Public Notice on September 30, 2016 clarifying that voice service providers may block calls using a spoofed Caller ID number if the number’s subscriber requests that they do so. The 2016 Guidance PN built on the Commission’s earlier clarification, which, among other things, clarified that nothing in the Communications Act prohibits voice service providers from offering call blocking tools to those consumers who request such services. Following from that initial guidance, the Strike Force Report sought additional clarification regarding the permissibility of certain provider-initiated call blocking. Specifically, it sought clarification that 1) providers may block calls where the Caller ID shows an unassigned number, and 2) providers may block calls that the provider has determined to be illegal robocalls, so long as the provider takes reasonable steps to confirm that the calls are illegal.
And to state the obvious, some of the robocalls violate the Telephone Consumer Protection Act and Truth in Caller ID Act of 2009. Additionally, if the inbound call is carried over a person's or business' VoIP or computer network, then it could violate Computer Fraud and Abuse Act also.
And I am also aware of the illegal spying campaign carried out with the US government. However, it literally took an act of congress to let the carriers off the hook for that illegal activity.