I know everyone keeps saying that they are only interviewing for alternate spots. I can tell you that I interviewed on Feb 2nd. They also gave me the opportunity to interview on the 13th, but I chose the earlier one for obvious reasons. I got my acceptance on the 13th and the word alternate never was mentioned to me by UoP, only by students on this forum. So I can tell you for sure that all interviews are not just for alternate spots (again as of last week).
However...
They are indeed interviewing for alternate spots along with class spots as of last week. The lady lets you know when she calls you if you are coming in for an alternate spot. There was a guy in my interview day that said he was there as an alternate. If I would have only listened to people here on the forum I probably would not have even gone to the interview so it was a good thing I called and asked.
My opinion...
If you have not heard from them yet I would not get my hopes up too high for interviewing directly for a spot in the class. I'm sure they are close to filling there spots.
However...
I would not give up hope of being contacted for an interview for an alternate
spot. The rumor that I have heard is that the alternate list is waited so if you are a competative applicant (competative applicant being a very subjective term by UoP and every d-school's ADCOM for that matter) you could have a good shot of getting in as I'm sure spots will open up...just not mine.