Yes, and this is precisely what is WRONG. The VoIP billing (the real one, and not the stuff from aimsoftwares you advertise) should always authorize the call based on the currently available funds and rates to the given destination. Yes, it is a post-paid service – but may be customer is over the credit limit already? Or may be his product only allows to call US&Canada, and he tries to call India?
So credit time should not be “high”, or “stoned” or something else :-), it should always be precise…
To others: this is exactly the reason why you should buy stable and mature VoIP billing from the reputable company with some experience. Otherwise you will pay out of your pocket for system architecture flaws such as the one above…