A couple months ago we reviewed SodaSnap, a free application for the iPhone that allows you to send postcards. SodaSnap didn't allow you much flexibility, and was definitely not an iCard replacement. However, Memento for iPhone and iPod touch [iTunes link], which brings Mail.app-like stationery to everyone's favorite mobile platform, is a better alternative.
Each "stationery theme" allows you to add one picture and some text to the message. When you open the application, you are presented with a screen that shows all the messages saved as drafts, plus the ones that you've already sent. To start a new message, tap the "+" in the top-right corner of the screen.
To add a picture, just tap in the gray area with the camera icon. A popup menu will ask if you want to take a new picture or browse for one in your photo library. Once you've selected the image, it will be placed in the gray area.
This application is solid and has some nice themes to choose from. There is still room for improvement, however. I would like to see more themes (the 14 provided themes are nice, but they get old after a while). I would also like to see the ability to add more text, as you currently can only add a small snippet to your message. This is one of those applications that is just cool, and it has a variety of uses. If you're looking to surprise Grandma with pictures of her grandkids, then this is the application for you. You can download Memento for $2.99 (US) from the iTunes App Store.