Well, to add insult to injury: as I hurried to get my new iPhone prepare itself to install the new iOS version, I just said "yes" and "no" or "not now" to a plethora of start-up questions, knowing that I would wipe them clean again with the migration, after that long awaited update. Unfortunately, it seems that several options like Find My and associated nifty security measures make it quite hard to just reset an iPhone.
So now I have to wait for a so-called cool-down period of an hour, before I can finally release the protection against stolen iPhones and switch off "Find My iPhone" and wipe all existing apps and data to eventually start the migrate procedure...
Don't get me wrong: I think Apple is very clever in implementing all kinds of security measures. But when things don't work as expected, any hacks or work-arounds are tough, making your misery even tougher. :-(