I wonder wether the properly unlocked device has to be the same as the one you hacktivate later. Perhaps I could use a friends' push.cert and push.key files... ? Or do you think two devices can't have the same .key and .cert files?

I have an AT&T sim card on the way from the USA, but I'm afraid I can't activate because of other people saying you have to enter your personal information in iTunes and go trough billing plans screens etcetera.