Cell takes place in the same world as Dollhouse
The phone virus that destroys sanity seems awfully familiar, don't you think? Its origin is never specified in the book, but we all know that the Rossum Corporation is the real source, right? Randall Flagg had some sort of involvement.
We know Randall has aided a bit in the destruction of another reality on a similar scale. We also know that survivors had dreams of him. Seems kind of odd that an "apocalyptic cowboy" is also mentioned, as Clayton Riddell may be tied into Roland and his ka-tet's adventures, much like how Stephen King is. Randall Flagg Is the Raggedy Man
The Raggedy Man AKA The President of Harvard is this worlds incarnation of Randall Flagg.