IT staff per User ratio

Could anyone provide an idea of what a typical ratio of IT staff (administrators) per users would be.

We are a typical small/medium business environment with MS products, Exchange, Proxy, Windows NT workstations, full range of desktop apps. We have an internal user base of 16 at present which is to grow to about 30-40 quite quickly. Our IT staff are expected to support a Customer Call Center of up to 30 staff.

We also maintain our own Internet Servers, routers and firewalls.

I’d appreciate any feedback from any IT Managers out there outlining how many staff you have per supported user.

Thanks in advance.