Probably the best asset of a telemarketing company is how its staff communicate with the clients. This is the soul of the trade, this is how they do business. Watch this funny but very effective way of convincing your client to do business with you.The effectiveness of an employee to do business with their client is the greatest, and probably the best way of nailing that deal down. In serious terms, it is this skill that the company pay you for. If you can't create a good impression, good relation with your client, then you do not have a room for this kind of business.
For many years, even before Telemarketing, offshore outsourcing and call center firms were invented and established, sales talking has always been used as a means of selling things.
Even in your local malls and supermarkets, sales clerks are trained to communicate with the customer, let them know why buying the product is good for them, what good using their product will give their customers and how would they benefit from using their product.
For business like Insurance companies, where agents roam around the place, go door-to-door and explain things to customers, they need someone to hire that is good in communication skills. For fast food chains, aside from the fast and good cooking abilities, their crew must also know how to convince their customers to "Go Large" and upgrade their drinks and fries to bigger sizes.
Now, would you like to up-size your drinks and fries with free toys, Ma'am? :)