This is from last month, just noticed.
....the FCC says 2,411 of these providers “failed to properly file in the Robocall Mitigation database, and must now show cause why they should not be removed.” In other words, these VOIP companies are lightning rods for spammers using their services to spread illegal calls, and they’ve ignored federally mandated action to stop spammers from pestering and scamming Americans.
The FCC’s authority over conventional phone calls is basically absolute, and this action was taken in partnership with attorneys general from every US state and Washington DC. If you’re a company providing call service, whether over standard networks or Voice over IP, you have to comply with the STIR/SHAKEN protocol for caller ID verification and you have to send the FCC a robocall mitigation plan. The FCC alleges that these companies have failed on both counts and missed multiple deadlines for compliance checks.
https://www.pcworld.com/article/2553377/fcc-threatens-to-block-spammy-voip-services.html
Full list of companies:
https://docs.fcc.gov/public/attachments/DA-24-1235A1.txt
Of the thousands of companies on this list, a quick look suggests that the only ones well known to us here are Axvoice and Nettalk.