I think it depends how you're placing your lower-tier version. If it's permanently free, I don't think you need credit card information. If it's a 30-day trial

I think it depends how you're placing your lower-tier version. If it's permanently free, I don't think you need credit card information. If it's a 30-day trial of your paid version, you might want to grab the card just to make sure that no one's signing up, waiting a month, canceling, and creating a new account. I'd recommend not doing the "we'll charge you unless you tell us not to" version. Just make it really easy for them to buy it when the month is over.