Finally managed to plug the iphone to a computer with iTunes.
Through that I got the firmware installed (as I said, the phone had completelly blocked) and managed to obtain the owner's phone number.
It's a US number (as suspected) from California (area code is 707).
UPDATE: Thanks to google, tracethatnumber.com, peoplelookup.com and reversephonedetective.com even got the county and city in California (not disclosing!). OMG that's really scary!
UPDATE (aug 24 2009 19:00GMT): If you are the owner or know the owner CALL the lost phone! We've managed to unblock it (actually iTunes reinstalled software from scratch without even asking). I'm waiting for your call.
UPDATE (aug 25 2009 11:00GMT): The SIM appears to be blocked again. Can't make or receive calls anymore.
