so can you pay with visa gift card

Sometimes it doesn't accept them. You can choose "pay with paypal" option, then use your giftcard as your payment on paypal. That's how I do it.

You have to buy Italki Credits, but that should work with any Visa card, regular or prepaid. http://support.italki.com/entries/21577102-How-do-I-purchase-italki-credits-