This sounds, to me at least, as though your stbx is trying everything possible to keep the stress level high. If he really wanted to talk to his son, he would call regardless of when. He’s trying to control the situation.
You have done the right thing by letting him know that he is welcome to call at a designated time. If your court order does not specify anything about telephone communication, then it is up to the parents to work that out. You are not violating the order by requesting that communication be initiated by the father. If your son were a little older, I think it would be alright to have him call his father. Since he is so young, it would actually be you calling him. Actually, it sounds as though he’s hoping that the name of your roommate will show up on caller ID or that he’s going to attempt to show the court that you are refusing to allow him contact with the child.
Since he has forbidden you to contact your child during his time, then I would suggest that in the next e-mail you put in a scheduled day and time that you will call your son while he’s with his father and that will be the same schedule that he is allowed to contact the child while he’s with you. Ex: “You can call on Wednesday anytime between 6:30 and 8pm. This will be the same day that I will call our child while he is in your care. If the phone calls take place at any other time, I can not assure you that he will be available for you to talk to him. If we can not agree on this, there will be no guarantee that there can be any communication between you during my custodial time.”
If you are bending over backward to try to accomodate him and give him the necessary time with the child and he is not working with you, then joint custody can not work. Joint custody can only work if the parents are able to communicate and work together to raise the child separately. It’s a constant struggle and the child’s best interest should always come out on top. But as with most ex’s, yours sounds as though he’s more about keeping stuff stirred up than about what’s best for your child. Unfortunately for you, you must put your foot down on every little detail until your stbx understands completely that your life is no longer his concern.