I think it can be helpful to call the program you've applied to, but granted it depends on who you speak with and inquire about your decision with. I've called admins and contacted the Director of graduate admissions, and received a status update. It can really depend on the program though, whether you have been accepted, rejected or even wait-listed. Once, for one program I hadn't heard back for a whole month!! I called periodically to speak with office staff and they were unfortunately not very helpful, just stating the generic "Decisions are still being processed!" I decided to contact a PI who I met and who was on the admissions committee--he informed me that my application was on hold (it had neither been rejected, accepted, nor waitlisted) and he advised me to keep calling to inquire about the status since the admissions committee would be meeting again to discuss the applications on hold. He also said, and I quote, "The squeaky wheel gets the grease!" I got an acceptance the next week! So have faith, patience, but also a healthy sense of importunity.