A lot of billing systems are organized around event delivery. The system does what it does and reports usage. This reporting is asynchronous and can be done E.G. via cron jobs running on a 24 hour cadence in certain cases. There's an internal guarantee that billing records for a given period are delivered by a certain time. Nobody checks whether the user has enough money to do what they're trying to do, just whether they're authorized to access the system in the first place. Shutting down accounts due to non-payment is more of an abuse / fraud concern, and happens long after the bill is delivered.
Wow, I wish my my cell provider worked like that! Instead, they somehow manage to track and bill me literally in real time. How do they do it? Do the telcos have some magic pixie dust or what?
Telcos did work like that (especially in roaming scenarios).
Your MSC (roughly the thing that people in your geographic area connect to) would talk to your HLR (the place where your records are stored specifically, regardless of current location) to authenticate you and make sure you're a real subscriber, but it wouldn't necessarily do so before every single call. At the end of some billing period, the operator whose services you've used (MSC owner) would send billing records (using the TAP format) to your operator, usually via FTP or similar, and your operator would use them to send you a bill.
This worked for post-paid, when customers were assumed to be trusted, and legal sanctions could be levied against those who refused to pay their bill. However, this approach broke down when prepaid plans were introduced. This led to the invention of CAMEL, which is basically a realtime protocol which lets the MSC ask the HLR whether a given call was permitted or not.
> This worked for post-paid, when customers were assumed to be trusted, and legal sanctions could be levied against those who refused to pay their bill. However, this approach broke down when prepaid plans were introduced. This led to the invention of CAMEL, which is basically a realtime protocol which lets the MSC ask the HLR whether a given call was permitted or not.
And since the cloud providers don't have the problem in your first sentence (even if the customers pre-paid, they're still easily identifiable), they never bothered to implement the solution from your last sentence. But seriously, the problem of accurate, real-time billing is not a new one, and it's been solved before several times already (e.g. RADIUS/Diameter of dial-up ISPs).
