I worked for a mobile phone operator many years ago. I was there when the company was bootstrapped. We built our own billing system because we would be billing for stuff that incumbents didn't bill for, because they didn't offer those services: we were the first 3G operator of the country and we also had to create and sell contents (example: YouTube was not born yet.)
I was not in the billing team but we definitely followed rule #4 of the post: "You must be prepared to staff an entire team".
And yes, #1 "Pricing changes all the time and billing needs to follow".
About #2 "Your billing system needs to scale with your user base", we had to go from 0 to 3 million customers in 9 months to be viable. We were not typical, we made it.
No idea about #3 "Grandfathering causes headaches" but there were probably many headaches, that one and others.
I was not in the billing team but we definitely followed rule #4 of the post: "You must be prepared to staff an entire team".
And yes, #1 "Pricing changes all the time and billing needs to follow".
About #2 "Your billing system needs to scale with your user base", we had to go from 0 to 3 million customers in 9 months to be viable. We were not typical, we made it.
No idea about #3 "Grandfathering causes headaches" but there were probably many headaches, that one and others.