Hang on a minute, Salvador Dali's work is Art! Every telco billing system I've seen, and I've seen lots, are the product of some sales droids enthusiasm to get their grubby mits on as much of your money as possible by means of confusion marketing, combined with their complete inability to notify the billing department of what they're up to until customers start phoning up complaining about the bill. In fact the confusion is usually so extreme that no one really knows what the bill is, and it generally falls to some sort of agreement or acquiescence on the part of the consumer as to how much you pay, and then the billing system is quickly written using staff of dubious ability. Then you get the next wave of complaints on these bills, and they get some slightly more experienced staff to try and sort out the new mess.
Eventually they end up with loads of highly experienced contractors, who spend their time tinkering with the systems in an effort to minimise the number of customer complaints, and still maximise the take for the telco. Although it is hardly ever described in that fashion.
Then, every so often, some management type decides they're going to save loads of money by unifying their billing system and getting rid of all the contractors. Sounds and looks great on the PowerPoint slides. Unfortunately the management droid has to look up what POTS means by use of Google, so their understanding of the situation is likewise vast, not! So they get a new system, written by a bunch of part-time college students, some of who do actually study IT, so it does at least compile..
Then they get contractors in to sort out this next mess.
And so it goes.