Honestly, since there has been NC since the call then the message has been received and likely best to just leave it at that.
My H placed a call as well. I would have preferred a letter but had no clue what I was doing - this was before I found SI!
Anyway. She has broken contact approx. 8 times now but some were work related. We should have clearly outlined boundaries with regards to work. Anyway. He is changing his cell and we will be seeing a lawyer if she contacts him at the new #.
In some ways it might be good for him to write the letter, show you, add to it and then put in an envelope ready to go "just in case".