Quite a few of my friends have done telesales work (cold-calling people). The hours and pay are terrible, there are few opportunities for promotion and you get abuse from people all the time. Also, you get extra money for the number of products you sell, so that is probably why they are so pushy. So yes, do have fun messing with the sales staff. I would guess that leaving the phone off the hook probably does annoy them quite a lot.