I'm not saying you're wrong but a) this sounds like a massive safety issue and b) this sounds like exactly the sort of thing I'd say to anyone trying to get a dodgy phone card from me, "yeah you need to wedge your foot in the door in case it detects the card is hooky, and tries to lock you in" just so I could stand there and laugh at their contortions trying to keep one foot outside while they use the phone.