There's been a lot of speculation that maybe PRISM doesn't take data directly from private company's servers, and that all the denials you've heard are carefully worded to deny only direct access. According to this new PRISM slide from The Guardian though, the NSA does have its hooks directly in the companies that are denying it.
And it's not just direct access either. The slide also indicates that the NSA has its sniffers upstream, sipping on pure, unfiltered data from the pipe as it travels from point A to point B. That part however, isn't technically PRISM. And it's all topped off with the handy advice that "You Should Use Both."
This puts a bit of a damper on the theory that the companies who are denying PRISM are telling half-truths, and adds a bit more fuel the theory that they are just out-right lying. We'll just have to wait and see if anyone changes their tune. [The Guardian]