Set up a Call Center has many perspectives, First you have to know your potential market, Inbound or Outbound projects, Customer Service, Sales (TMK), Technical Support, Complains , Billing ops, etc. Because the kind of market you want to target define the invesment you need to do it. You can start with a PC-CTI which is a complete set up tool for your Telephony needs, but has limitations, let say for large project or big companies, probably they won´t accept this tool and they will need the typical PBX structure. And your budget will be very different in each scenario. I´m looking your point of views and Did you explore the huge hispanic market operated from outside of US, Mexico or South America It is a good options, because you have low operational costs and all the access to the technology.
I hope my comments works for you.