WARNING: this book is a PhD dissertation (2000) and contains academic research. It's made available primarily to aid other academics who are conducting their own industry research. If this is what you seek, here's an overview:  

The telephone answering service industry is maturing and undergoing rapid changes. In recent years, the traditional client has been vanishing, switching to alternative technologies, bypassing their answering service. Telephone answering services have reacted in various ways, such as mergers and acquisitions, pursuing niches, or expanding their businesses' scope. 

The conventional wisdom is that there will always be a need for the human interaction which an answering service provides. It further assumes that answering services will serve fewer clients and generate less revenue unless steps are taken to increase their reach or obtain non-traditional clients. Previous research has recommended becoming a call center to better tap and capitalize on the needs of an emerging non-traditional client base. 

The findings of this research effort determined there were the essential elements which should be present for a telephone answering service to transition into a call center. Additionally, there were five items which are common industry dilemmas to be addressed. An inventory of significant call center characteristics was also developed. Most importantly, several areas of focus were advanced.