Anonymity can be achieved by going to different public buildings that you can access telephone jacks in, (unseen and unrecorded by camera). Wear a wig and sunglasses when you go there and then put on a ski mask before you enter the building (preferably at night time). The BBS server software should accept anonymous postings and anonymous logins. Security can be achieved by writing the BBS server and client software to implement some type of TLS connection and transmission communications scheme. Finally you should be able to use this system to publicly post pgp/gpg encrypted messages on the bulletin board, where you pre-share signed keys by hand with local recipients, and leave the messages for the pseudonym of your recipient to flag the message for the person who should copy it and decrypt it ( on their air gap after copying it to a floppy and shuttling it over to their air gap decryption station).

Every city in North America should have 10-30 of these encrypted telephone BBS's running, and the whole mass surveillance problem will fall apart. Also you can setup telephone peer to peer encrypted communications from 8 bit computer to 8 bit computer, and skip the public posting part and have authentication to post on your machine and exchange the pgp messages that way. So I email my friend encrypted over the telephone network dumb machine to dumb machine and leave a message (So what if it's recorded, ooooooh you know that I called my friend from school in town, good for you, but its encrypted so unless he's a rat you don't know what we talked about, and when the machine is power cycled, its gone off of the dumb machine, wiped from memory, poof, gone).