Yep, we are being deprived of our privacy more and more in this electronic society. It's true that by linking the Octopus card, it sure gives you some limited amount of benefits, e.g. cash rewards, etc. but then next thing you know, the telemarketers are calling you all the time while you're having dinner.
Does HK have the "No call" registry? Once a phone number is registere with the authorities, telemarketers are prohibited to make sales calls to that number? Violations can be very costly (to the telemarketers).