Telephone harassment is a crime in here in Colorado. It actually falls under our stalking statute. Has she tried tape recording any of the conversations? Has she tried reporting this to the police or local district attorney. She might want to get a restraining order. If the guy can't speak civilly to her on the phone, maybe a motion to restrict (as in suspend) his visitation. If he is behind on child support, she can report this to the county child support enforcement. If she is on base, he may have committed a federal crime. Since you are deployed, she may also want to contact the closest JAG office. There may also be some volunteer lawyers in her locale willing to help her out. We have such a program in Colorado.
Let me know if you have questions about any of this informal discussion, which I must emphasize is not legal advice.
Most importantly, thank you for your service.