One of the better pieces of advice is: Never let your teen make a decision that might involve money.

This may recently have crossed the mind of a Florida father whose teenage son ignored an alert from AT&T while using the iPhone service his dad pays for.

Son Ashton Feingold told CBS Miami this week that the friendly warning "just said, maybe 65 percent of your data has been used."

I can't remember ever getting a text from AT&T that included the word "maybe." Still, Feingold says he ignored the alert because he'd gotten such warnings before with no dire consequences.

This time around, however, his dad received a bill for $2,021.07.

The two blame Apple's Wi-Fi Assist feature. This automatically switches your phone from Wi-Fi to cellular if it decides your Wi-Fi signal is too weak. It's on by default in iOS 9, a recent version of the software that runs the iPhone.