I got a phone number from ATT. It previously belonged to someone who had collection agencies all over them. Some of them left phone numbers so that I could call them and tell them that it was no longer the debtor's phone number. But most of them would never identify themselves and just hang up if I tried to explain anything.
For these guys, I just answered the phone by saying, "you are being recorded, please state your identity." (I only have the number for DSL so I didn't have to worry about freaking friends out. Can I get rid of my ATT phone line and still have DSL? At the time is required.)