Staffing Model

I recently read an article in TechRepublic called, "How to Rightsize your IT organization." I am a Telecom Manager looking for a model that will provide me with the correct number of staff "experts" across the skillset functionality that combines design/installation and problem management/break fix. The article provided a spreadsheet, which I thought would work for me, but it really does not provide industry benchmark standards that address a combination of IP enabled and legacy system. Can anyone out there tell me if there is a better way to identify how many Techs, System Specialists and Developers a company needs based upon known quantities, such as servers, applications, systems, number of desktops to support, etc?