I have been subpoenaed and put on call. do i have to show up if the attorney doesnt call me?

I was subpoenaed to court by a friends' attorney. My friend is the defendant. The subpoena says I'm on call. The attorney called a couple days ago and said he would call if I'm needed. So I'm wondering if I have to show up tomorrow. I'm in Oklahoma if that helps anyone answer. Thank you!