Applicability of Early Action/Early Decision to PhD admissions?

Hello,

I was wondering whether the concepts pertaining to Early Action/Early Decision are applicable to graduate school admissions as well, especially for PhD. From whatever I could gather from net, it seems solely applicable to undergraduate admissions, still I wanted to clarify once: Are these concepts relevant for PhD applications and if yes then which universities offer such choices? I couldn't find any top ranked uni in an informal list that I went through.

Thanks in advance.