Simple , if you have one phone number for the place you both live in as in regular phone service and he has a cell phone Change the house phone number and NEVER call her from it with out dialing *67 first ( test it out calling a cell phone so you can see the call ID, if it says not avail or private then its fine to do it that way , If she will not accept private calls then he needs to use a cell phone, EVEN a prepaid one will work , then this way he can look at it , see it is her and let the voice mail get it when he cannot be disturbed and have the phone co change the number on the house phone and pay the non published fee so it is not published in 411 services. This way he is able to speak to her about the kids, he can save any messages that he needs to and you will be free of the problem, IF you cannot get a cell phone then ask the phone co for custom ringing , they stack a whole new number onto the same line , it has a different ring pattern when callers dial that one , when that one is dialed you would hear the different ring and be able to answer the phone with out checking call ID and know it is for you.