Outsource Tech. HelpDesk

Hi all,
I am new to the callcenter arena, and i want to know the the network connectivity from the US end right upto the Call center premises.
I want to know if ISPs can take an IPLC from VSNL and lease it out to Call centers.
Also, can the ISP carry voice traffic from the call center or he has to give bandwidth IP based callcenter only?
What are the exact components that go into the network? IF someone can give me a network connectivity diagram i will be obliged.

Thanks,
Kaustubh