During Apple's "Let's talk iPhone" event that is going on now at the Apple HQ, Scott Forstall just got done announcing the Cards app.
No, it's not some type of new poker game. "Cards" is a service for your iOS device which lets you design a greeting card on your Apple phone or tablet and then Apple does the rest for you.
When mailed within the US, the cost is $2.99 per card. What is interesting is that you also get card tracking on your phone, so Apple must have sorted out some cheap rate with Fedex or such to offer tracking. The "Cards" app will be available on October 12.