I can't really tell you much. I have been in contact well some faculty members at some of the schools I've applied for and none of them have mentioned that interviews were a part of the admission process. Furthermore, I know that most schools have just begun the process and are just commencing their preliminary filtering. MIT and Carnegie, for example, have not even finished sorting the application materials.
I applied only to Top 20 schools, so I don't know anything about lower rated schools, but, here's what I know regarding the application process at NYU as explained in the open house they conducted:
1. In the first stage, the head of the finance admissions filters the applications down from 350 to 50.
2. In the second stage, he asks four different faculty member to rate each application - thus narrowing down the amount to around 20.
3. Final decisions are made in coordination with the head of the PHD program and eventually 9-10 students are offered admission and around 5-6 are enrolled.
As far as I know, top schools do NOT offer admission on a "rolling basis", that means that all admission decisions are made all at one time.
I believe that most schools are only now in the preliminary stage of filtering the applications. I assume that the process is different in lower rated schools who receive much less applications.