Telephone!
I have a French telephone and phone number - I am practically a part of French society now. Or something. It's a cheap, ugly phone that doesn't seem to have an off button (if anyone has ever had a Nokia 1650 and knows how to turn it on and off, please let me know...) but it's mine. And it means that I don't have to pay to receive phone calls anymore!
And when I get back to the UK, I need to tell T-mobile to unlock my proper phone, so I can use something sensible and non-ugly again...
EDIT: Apparently one turns it on and off by pressing the hang-up button. Of course. Why didn't I think of that?