It seems pretty clear that the mobile operators are the biggest commercial organization threats to personal liberty. Their only real competition is the banks.
Cash is really easy to use and is accepted everywhere. There's no similarly elegant solution for mobile connectivity if you want to stop revealing metadata information.
Given the number of network connected machines that cash passes though (ATMs, ticket machines, counting machines, ...), I'd assume that such machines would be routinely scanning the serial number of each note. Couple that with an account number, or the CCTV that is usually pointed at any cash handling machine, and I'd posit that the anonymity of cash is eroding.
> "Legal tender for all debts, public and private".
Yes, debts being the operative term here. You don't incur a debt until you receive the product. Airline tickets are paid for in advance so the customer never incurs a debt.
