So far the consensus is that "Smart Limits" is not so smart or so limiting.
You can place free alerts on any of the phones on your plan, as well as a total usage alert on the account. You will be notified by text.
Mom tip, one parent to another...
1. Make sure your son understands what is using mobile data and when.
2. Go through settings on his phone and turn off cellular data for as many apps as needed to comply with his data usage cap. This is the same place on his phone which will tell you what apps are using a lot of data. Very educational! Social media apps have settings within the app to restrict video to wifi only.
3. Once you have covered all bases, put it on him (been there). Use the data alerts to keep you both informed and if he reaches his limit, you can turn off mobile data to his phone online. It will not effect his ability to call or text, just no mobile internet use. From experience, it will happen once, then he will learn you mean it.
Isn't parenting fun?