Well, I left it plugged in via USB and charging. iTunes was open. Nothing unusual. Until an hour or so later, out of the corner of my eye, I noticed a zooming shiny apple animation, picked it up and was prompted to "Set up my iPhone". Ugh. I haven't backed it up for 10 days or so and there's stuff on there I really want to keep. So I went through the setup, enabling location, selecting my router, and then trying to activate the phone, all the while hoping once completed everything would be just as I'd left it, right as rain. But I can't get past the activation stage. And when I opt to activate through iTunes, iTunes complains that the iPhone's software is too old. At this point I should mention I'm a registered developer, and my iPhone was running iOS 5 beta 3.
When plugged into iTunes it displays 8.7 GB of space taken, all marked as "Other", and it's still on build version 9A5259f, i.e. beta 3. So I'm reasonably optimistic my precious data's still on there. But I can't use it to see. And when I try to back it up now, nothing happens.
I'm guessing this could be because beta 3's expired? Maybe? I didn't get around to updating it because for some reason over the air updates wouldn't work. Any advice on what my next move should be would be very greatly appreciated!