Activation and first month on your new phone. Sounds right. There is no incentive or credit to keeping a phone past 50% paid off when it is upgrade eligible. As long as you hit 50% paid you can get a new iPhone, which is why the program is so alluring to those who update on launch every year. Like leasing a car, you pay a little more for less time, though you lose a percentage of return if you owned that car outright, then sold for private values. The benefits win, and you always have new, fresh, under-warranty property. Always get insurance!
You still used it for that 75% of your two year term. Looks right.