These guys called (name of Andy) and said they could lower all my credit cards rates to 5 % for life. They were just phishing for information and I was amazed at how much info they had on my cards and balances and even last payment made. Don't give them any info just hang up.
It really is not quite as simple as it may appear to stop this although you are right there is tracking information the telecom uses for accessing fees for service. These guys are using VOIP and then entering the phone system locally with any ident or number they wish, in some cases the number is valid for some person and people call and insult this person thinking its them. Personally I am getting to the point of trying ooma.com as gets rid of them and sends a signal to the telco that they need to address the issue.