Different schools have different "rules" for how this plays out. Most top schools will have a notification date and will not release information prior to this, whether written or on the phone. I would say it is highly unusual for a school to roll out announcements on their offers prior to their announcement date. You can imagine that if they did, they would be inundated with calls from prospective candidates. Sticking to their announcement dates keeps both the applicants and the schools themselves organized and in control.

Generally, schools stick to their policy that they notify applicants on the decision date. I've heard of a couple of cases, however, where candidates were called days ahead of the deadline that they were accepted. These are exceptions though. Most schools might not do this at all. You will probably never get an early ding - so any early news will be good.