I have seen their are call center in Karachi,but unfortunatly they are few call center who know how to use them in a proper way.
1- The staff working in a call center should aware of the product thoughrly and able to sell them by providing them the benefit of the product.
2- It just not be an order taking center,staff should be carrying a convencing power to sell the product.
3-Comunication very much esential between staff – customer and line manager.