Call Center – Multi-site connectivity

I am looking for feedback on the evaluation points between two call distribution methodologies for a multi-site call center: CPE based point to point network vs. PSTN based take back and transfer routing. Circuit switched solutions. VoIP is not under consideration at this time. I wish to establish the critical evaluation factors as well as get feedback on possible weighting of factors. Finally, I would like any case history information that can be shared.
* Costs – Capital costs for additional infrastructure and OA&M costs VS. network transfer charges
* Fault tolerance and redundancy
* Routing flexibility
* Impact on CTI and call reporting