My main concern would be giving a credit card number to an unknown person who called me. Secondly, many VOIP providers have telemarketer lists plus allow you to block calls of specific phone numbers not already being blocked. The problem with that is, like someone else mentioned, they use voip with any NPA/NXX they want and after hauling ass, set up with new phone numbers which you once again have to block. It just never ends even if you call route their number to a disconnected phone action which with my VOIP provider, VOIPO, gives a recording from the caller's phone service that the number is disconnected or "no good". If a telemarketer is actually a live person, which you determine by Googling the number, I forward the number to a Humor Hotline phone number with an appropriate recording. Example: 2144711194