The article was from about a year ago, so I am not certain if anything has changed. The writer, Bob Tedeschi says,
"Amazon will refuse to accept a returned phone. And if you cut off service or switch to a cheaper plan within the first 181 days, it will charge you up to $250, on top of whatever early termination fees you face from the carrier. Walmart.com and Wirefly will charge similar fees if you end your contract early, so ask about that before you buy anywhere online, then decide if it’s worth the risk."
If I were you, I would call Amazon first. before making the purchase.
AT&T ETF is $350 + cost of first months bill.
Amazon's ETF is $250 if the plan is discontinued, switched to a cheaper plan or cancelled within the first 180 days.
You may as well go in and buy it at no commitment $499 at an AT&T store.