I used to interrupt them, and then go into my song & dance about what my company sells, breaking the routine often to ask them if they thought it's a good deal they can't live without.
Now, I've evolved to become an interested potential customer. I kept the caller from Shaw on the phone for about 20 minutes with questions they couldn't answer about the high speed Internet service they were flogging such as, "What is the upload speed? How does your light version download bandwidth compare to your higher priced product? What model of cable modem do you install?"
They had to go ask someone for the correct answer every time, until finally I begged off for now and told them to try back in a few months.