In our case, implementing a pay for call, or even an account number would have been fairly hard, as an 8 person company. MOST people respected it, and on top of it there were a few cases where people used it to our benefit.
So, it was definitely a judgment call about if we should add something requiring a special code for access, charging, etc... In this case, we had to make the judgment call about implementing something like this, or stopping public NTP service.
Part of the equation also included that pool.ntp.org was now available and fairly well populated, when we started offering NTP service it wasn't a thing.
It is what Microsoft does. Even with a support contract, you have to provide them with a credit card number before they will accept a support case. When Microsoft agrees you've found a genuine bug in their software, they won't charge you.
So, it was definitely a judgment call about if we should add something requiring a special code for access, charging, etc... In this case, we had to make the judgment call about implementing something like this, or stopping public NTP service.
Part of the equation also included that pool.ntp.org was now available and fairly well populated, when we started offering NTP service it wasn't a thing.