There is a way to use your Visa card to purchase train tickets on www.trenitalia.com. First, you must be registered on www.trenitalia.com. Second, YOU MUST BE REGISTERED on the Verified by Visa site. Trenitalia is a participant in the Verified by Visa program.
HOW TO REGISTER WITH TRENITALIA
Go to www.trenitalia.com. Select English in the top middle center of the page. Select "Register Now!" in the For Passengers section. Fill out the required information. Trenitalia will immediately send you an email with a temporary password. Immediately use this password to sign on and create your own new password. My experience was that the temporary password doesn't last too long. Once this is complete, you are registered.
HOW TO USE VERIFIED BY VISA
Visa has a feature called Verified by Visa. It provides an additional level of security for on-line purchases. If you have a Visa card, you can register it on the Visa site. CLICK HERE for the website. It has nothing to do with the bank issuing the card. To register, you will be asked to enter the card number and other info to identify yourself. Then, you will be asked to provide a short message. That's it.
When shopping at Verified By Visa websites, a pop-up window will appear with your message and a space for you to enter this special password. I've been registered with Trentialia for 3 years and used to be able to use my Visa card. It stopped last year. Now that Trenitalia is a Verified by Visa website, I was SUCCESSFUL ONCE AGAIN in using my Visa card to purchase a train ticket online. Note that you can choose to print out your ticket at home. The ticket has a PNR number on it that the conductor will enter into a wireless PDA for verification.