Will my Korean iphone 6 be eligible for trade in?
I bought this unlocked iphone 6 when I was in Korea so I am not sure that my phone is still eligible for Apple's trade-in.
iPhone 6, iOS 9.3.5
http://www.apple.com/iphone/trade-up/
You would probably make more money selling the iPhone 6 privately
and then apply those proceeds towards the purchase of your next
iPhone.