A calculation is a planning aid
A voice bandwidth calculation estimates traffic under stated codec and packetization assumptions. A power budget compares device allocation with available switch capacity. A cost comparison depends on included services and administration effort. None of these measurements alone proves production readiness.
Start with the existing business calculators
Use the business cost calculator to structure service-cost questions and the network readiness calculator to frame your connectivity review. Keep the inputs with your planning notes so another person can understand the result.
Use conservative inputs
Count simultaneous call legs across the relevant link, not just registered devices. Separate per-port power capability from the switch's total available power. Include setup, recurring service, support and administration when comparing platform costs.
A percentage allowance is an explicit planning choice, not a universal engineering margin. Model a normal scenario and a busy scenario, then validate the actual peak workload. Leave room for other traffic and equipment sharing the infrastructure.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.