I do believe your STBXW is just reacting and stirring things up.
Having calls during your visitation time depends on the schedule. You say visitation week, and you have 50/50 custody. So, I assume 7 days on and 7 days off. A call in the middle, say Thursday, is not unreasonable. This is exactly the arrangement some people at work have.
If the schedule was like some other friends (gosh, there is a lot of spilt families) a couple of days on then a couple of days off, then there is no need for a visitation phone call, she could wait the 48 hours.
Whatever arrangements she wants, she needs to realize you would also have that right or privilege. Not sure which to call it, since it depending on how cooperative you both can be.
Advice: Talk to the kids. I know they are young, and are upset with Mom. See how they react to the idea of Mom calling them in the middle of their time with you.
She is their Mom, forever. A call from Mom, a call from Dad, during the opposite weeks could be a very good thing for them. You are also there and can see/hear first hand a bit of how she is with them.
I would discuss the idea of allowing a call during the off weeks. She will be talking to them within days anyhow so making her wait isn’t really preventing anything. This arrangement does have benefits for you too.
If you are concerned for your kids welfare, you are beyond the considering of a weekly phone call.
I suspect she will tire of stirring up things if there is no splashing around. Also kids have a fantastic ability to innocently speak the truth, and say if they like someone or not. Mom may not like what she hears that often. Mom may call less or might even change for the better.
Look for a resolution that has good intent and kids’ interests at the heart of it. As long as you are not doing it out of fear, vengeance, or spite; I’m sure you will find a good answer.
All else being equal, I’m for allowing a call.
DnJ
Feelings are fleeting. Be better, not bitter. Love the person, forgive the sin.
