I applied to UTD for Fall 2015 and they sent out the acceptance letters in waves. So most likely they have sent out the first wave and are allowing those accepted a certain period of time to accept or decline their offer. They will continue this until the class size is full. Hope this is helpful!
Let me know if they respond with any helpful information! I just hate that they don't give a rank, nor do they give you any insight as to when you might hear.
I'm still waiting to hear too and starting to get discouraged. Someone posted they got off the waitlist on the results page, I'm just hoping they haven't all been sent out yet. I checked the new Facebook Group for admitted students and there's 15 people in it as of right now.
I'm currently on the waitlist at UNT too. I saw on the results page that someone had been accepted off of the waitlist April 22nd but I still have not heard anything.
I haven't gotten an official rejection by email or mail but my portal updated to denied. So if you're still waiting I would go double check your portal on UTD Galaxy.