Never say "Always".
if the company is, for example, a telecom operator trading voice minutes or data capacity, or a non-telco company in a wholesale supply chain, their financial systems sure enough must support macro economics. Buy and sell.
Micro economics is just a special case of macro economics.
Good Morning Everyone,Nice healthy comments from all tmforum members surely add knowledge to everyone.I would say that for small csp's, it would be good to start with open source billing stack and then with the passage of time, need to do deep analysis as per company growth.for large csp's, majors risks for them is data protection, security, reliability, sla/support/managed contract and reliability of vendor for long term. All these points lead them to consistent billing system vendor.Also, when we talk about billing system, we need to define boundaries as this definition varies from vendor to vendor or open source available platforms.for only billing and calculation, open source platform Kill Bill is also a good choice.