Are you an international student? They admit about 12 students each year. Phone interviews are usually for top international students. Domestic student have in person interviews during the visitor's weekend which took place about 2 weeks ago.
I don't think it is a good way to start a 5 year "relationship" with your new "home" (department) by asking them for more money, especially in this economy. I am sure you can get an internship in the summer and it will help a lot.
Which school would you choose for computer vision:
1. Boston University
2. University of North Carolina at Chapel Hill
3. University of Rochester
All with full funding.
It may be that you are on "waiting list" and they are waiting for admitted students to accept/reject their offer. You should see if students from your field were admitted.
I am still waiting for 12 decisions. UGH Why are they so slow - could they not reject me already:\ I hate waiting and making others wait since I can't make decision now;pp
At USC they only notify you by postal mail (the status on the website changes to "you should receive you decision soon" but I am not sure if it changes before you receive a mail - I only checked it afterwards.