[Jim727]

The key words here are "custody battle".

Dad needs to be careful - it sounds like evil mom is trying to gather data on him surreptitiously. I like the call-forwarding plan, personally. I'd give the original phone to dad's attorney and explain the tracking issue. If evil mom says nothing, then possibly there is nothing underhanded going on. If, however, she throws a fit because her "tracking" phone isn't the phone junior is using, dad can just tell her to call his lawyer.

And definitely be careful with emails.