ISDN modems were available in retail stores. Anything above v.34bis (ex: v.92, digital lines), required hardware, provisioning, and billing, at the CO. v.34bis and below simply used the available analog voice bandwidth (POTS), telcos resented that because the tech was popular and outside their control, but they did get to sell a lot more voice lines... dialup BBS and Internet. See... https://en.wikipedia.org/wiki/Hush-A-Phone_Corp._v._United_States https://en.wikipedia.org/wiki/Carterfone ISDN was also fun for... https://en.wikipedia.org/wiki/Caller_ID_spoofing Telcos *still* ban and resent what their users want to do. Which means some chance at profit still exists for startups building their own neighborhood, local, regional, etc fiber and wifi networks.