I got every single iPhone since its launch. I also sold every single iPhone that I use after I got a new one. I remember the day that when you upgraded your phone the other phone would go straight to your drawer and then straight to the trash.
Its amazing how much resale value the iPhones hold. This is not the norm for all other brands. Also the GSM models (T-Mobile/At&T) have more value because they work all over the world.
I see the same phenomenon with housing. If you picky the right unit in the right building it will appreciate more over time.
One good example was the Elleven building in Downtown LA.
After the crash most of the building had a 45% price correction. Units that were selling for $560k were ben short sold at $280k. A lot of people lost a lot of money.
One of my clients had the Penthouse there that he bought for $1.7 Million. We were able to resell for $2.4 Million in a down market. Not only he did not loose money, but he made a profit.
I understand that not everybody can afford the Penthouse, but it shows that sometimes paying a bit extra for something can pay off in the end.