We're currently reengineering our HR-practice, and planning to buy and install a HRIS this year. The consultant we're working with recommends us a service delivery model that includes a HR-call center. I would very much appreciate your sharing this knowledge. What you plan on undertaking is very expensive and time consuming.
Implementations take forever and usually cost more than planned.
Consider leasing software over the web and have someone else manage the data and calls. We, at The New York Times, have set up an HR Call Center. I do know that Texas Instruments and KPMG Peat Marwick have recently implemented such a center, and have had success. I would love to see any studies you get as a response to this. It is very interesting to my organization too.