I don't think I've ever upgraded my phone while the previous one was still operable :) That said, Apple is pretty good about making sure their phones fail on a

I don't think I've ever upgraded my phone while the previous one was still operable :) That said, Apple is pretty good about making sure their phones fail on a predictable timeline (2 years? Oh, time for the battery to stop retaining charge, or the touchscreen to stop responding, etc).