If the customer is calling within one area code, you might be able to do it. I had a stock broker* for a client, and they did this, but all of their calls were within one area code and for the most part within about four or five central offices.

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*Okay, technically, they were a slightly more respectable boiler room, that called rich old ladies and tried to get them to buy stocks. 4DNs on an SX200 D/L, with 2 phones per desk and a predictive dialer...