I get this quite a bit in my left arm from the shoulder to the elbow. The worst pain comes in the middle of the night and sometimes it's still sore in the a.m. I just chalk it up to sleeping on it as I tuck it under my head and getting older.

Maybe getting a headset would help you out, especially if you know it is going to be a long phone call (like calling an insurance company or some government office.). I hope you are doing better today.