So basically you're walking around with wifi enabled and you get a login screen around the hotspots? If you have 3g why don't you leave wifi switched off unless you need it, wouldn't that stop the problem?
It would.
Do you enjoy enabling and disabling Wifi on your device twice a day, every day?
A better solution is to 'Forget this network' on PCCW and PCCW1x. But it does make that 28 HKD a month rather wasted.