I am a bit confused about using IPLC links and T1 links in call centers. What are these and why do we need to use both?
An international private leased circuit (IPLC) is used to provide a private link over the Internet with a certain service level agreement (SLA). This ensures better quality then just building a standard VPN tunnel over the Internet. Here is an example topology where calls come in over T1 circuits in the United States. The calls are queued up in an ACD locally and then routed over the IPLC link as agents in India become available.
PSTN T1<-->T1 on IP PBX with ACD queue<-IPLC Link->Office in India with call center agents