Staffing levels

I’m analysing the staffing requirements for our call center where call time is~30% of agents’ time. Rest of the time is spent in emails, followups, faxes etc.

I have done a time and motion study and I have all the numbers and productivity levels in hand, but how do I go about planning staff levels? the Erlang Calculators do not give me the right number since the call time portion is low in our customer care center.