I don't know exactly what the process is, but my understanding is that OISE sends out letters for all official responses. So, when you receive a letter it is either a letter of acceptance, refusal, or a notice that you are on a waitlist. If you have been in contact with your POI then they can tell you (I think) "Unofficially" what your status is. You can also check on ROSI, the university of toronto's student portal, to see if you are "invited" to the program. If this is the case, it's sort of an unofficial acceptance before you receive your letter in the mail. That has been my experience anyways! I don't think you can assume you're automatically on the waitlist if you haven't heard, but you might be! Hope this helps a bit