Sources: NSA sucks in data from 50 companies
I think the best explanation is given here: https://news.ycombinator.com/item?id=5844576Prism is probably no more than a mail-merge program that will take your (i.e. NSA agent's) signed court order and convert it into whatever format each company requires. Then it will make the request quickly and easily - Say Google requires a PGP encrypted email, Microsoft wants a HTTPS PUT request, Facebook needs you to upload to SFTP server etc.