The update was noticed by MacRumors forum member techdude13.
"Poking around the website and checking my iPhone Upgrade eligibility, I spotted this "Trading in your iPhone" section, and saw something that made me truly giddy - a by mail Trade-in Kit"
Here's Apple's description of how the trade-in works...
Get your new iPhone shipped to you.
You can have your new iPhone delivered right to your door for free.
Trade in your current iPhone.
Once your new iPhone ships, we’ll send you a Trade-in Kit with a prepaid shipping label so you can send your current iPhone back to Apple.
To learn more about Apple's iPhone Upgrade Program, hit the link below!