If someone really doesn't like you:

They will put packet sniffer on their open network.
They will get unique MAC address of your device connected to their network.
They will secure court order.
They will force RIM provide PIN number for that MAC address.
They will find, using PIN number, which wireless carrier this blackberry belongs to.
They will force wireless carrier provide billing address of the blackberry owner.

Busted!

If they really don't like you...