One of the many "backoffice" costs voice service providers have to absorb into their pricing.
One of the many things associated with the evolution of telephone networks is the change in costs associated with operations and maintenance. With VoIP, we have transitioned from legacy copper based circuit switching to fiber based IP packet networks. The actual call control and media delivery is accomplished with software. Software has dependencies on computers and operating systems, which comes with cybersecurity vulnerabilities. So, as you're considering voice modernization, take into account that there will be a new "bill" you've not had before: The annual sustainment cost associated with software license renewals and software patching to maintain cybersecurity. Until next time...