"2 or 3 years after release"
Or better still, a fixed period after a model is discontinued. Three years from a model being discontinued should be the absolute minimum for a phone who's hardware and battery should last for that length of time. Of course if a manufacturer ensures that their software is good quality and re-used across models then the cost of doing this drops significantly.
But I'm not holding my breath.
Biting the hand that feeds IT
