Skipping the 7, I still have my iPhone 5 (not S ) and it is still working the same as it was when I bought it on release.
I'm pretty sure it wil hold for another year, then I will upgrade to the anniversary edition
I will get the 7 and then probably just do the one year trade in instead of the 2 years. A lot of people seem to think the 's' years are better. So if next year is a different form factor than in 2 years you will get the better one? I don't think it matters each new year has a better device than the previous. I am kinda excited about no headphone jack if it means a bigger battery or better waterproof. I haven't used headphones on my phone in a long time.