Determine staffing resource requirements given various call levels at a call center

What is the methodology for determining the number of human resources needed to meet minimum mandated service levels in a reactive, dynamic customer service environment?

Example: Customer Service Call Center (any type of business) staffing. Service Level requirement is minimal (< 1%) call abandonment (hang-ups) and responding (answering) all (100%) calls within 1 min). If we know the inbound average call volume range per unit of time (example: 1000-1500 calls per month, median = 1100), and the average call duration range (example: 5-30 min per call, median = 10 min), and 25% of daily calls occur between 7AM and 8AM, how should I calculate the minimum staffing needed to always meet service levels, and how does that staffing requirement vary as the percent of heavy call volume (the 25% between 7-8AM) varies?