I don't do this for phone calls but I do write things out if there is someone I need to convey something I feel is important IRL. I usually do this three to four days in advance and review and edit it many times as I usually come off as being aggressive and angry without even realizing that is how the other person is taking it. I also write things out when I am going to the doctor but usually just hand them what I have wrote down to keep for their records and don't have to stumble through reading it to them.