Can I request a different size SIM card when i'm on a contract with AT&T?

I have an HTC One X and it's badly cracking. I was wondering if I buy an iPhone 5 online for AT&T, if I can request a smaller SIM card since iPhone and HTC phones have different size SIM cards. My contract still has about a year left and I was wondering if it's ok to do so. And I read that it doesn't matter because I'm on a contract not my SIM card so it shoukdnt matter, is this true?

Yep they do it for free i would go into AT&T Store

You can get one from the store or request one via phone or website.

http://www.everymac.com/systems/apple/iphone/iphone-faq/iphone-sim-card-troubleshooting-upgrade-from-original-to-iphone-3g.html, read this. Was news to me.