Similar experiences to other. The guy (with an accent), said he was calling from VISA and could lower my annual interest rate. He had my name and address (which anyone with the internet or a phone book could get). He said all I needed to do was verify my account by giving him my credit card number. I asked why if he was from VISA, he wouldn't already have my full 16-digit account number. He told me that he needs to get it verified, and when I asked him to give me some information to prove he was from VISA, he did not answer but told me that even if it was a scam, VISA would not hold me responsible for the charges. Not very convincing. When I repeated to ask him to produce evidence that he was from VISA, he started to get angry and said that I was being stupid for not wanting my interest rate lowered. I asked him why VISA just didn't lower my interest rate. It's not like that would be bad for me. After a few more minutes of this song and dance, I hung up.
When I tried to redial the number that showed up on my call display, it was not in service (which almost guarantees it was not legitimate, because most legitimate companies, when you call the number back on your call display will either get voicemail or a pre-recorded message).