I applied to PhD programs last year, and if it's any indication of how other schools are, here's what I know from my personal experience:
Yale: Interview (contacted in January for interview)
Oklahoma: Interview (contacted in February for interview)
Colorado: Interview (contacted in March for interview)
Arizona: No interview
Illinois-Chicago: Semi-interview (contacted in March randomly by phone)
Drexel: No interview (although the website indicates otherwise)