By the way,my iphone6 mtn contract only 11 months old,can i get upgrade from istore?(MTN doesnt allow).... So only way is to purchase a new 6s by trade in my 6,is that correct?
This has been covered on the forum before, but I'm still not sure whether you can sell a phone that is still under contract - if you happen to default on the contract I guess the service provider could blacklist the phone.
Until you've seen out your contract period that phone isn't technically yours to sell. I'm sure the Apple store will want proof that the phone has been fully paid for before accepting it on trade-in.