Here's how Postagram works: Select a picture from your smartphone's photo library, Facebook profile, or Instagram account; compose a short note; and enter your recipient's mailing address. The image is printed out on thick, glossy photo paper at 300 dpi resolution, and pops out of the card as a 3 x 3-inch print.
Unfortunately, you're limited to sending square-shaped photos, which you have to crop yourself within the app. But Postagram is still a fun and easy way to give that run-of-the-mill postcard a more personal touch.
Each Postagram costs only 99 cents to send, which is cheaper than the built-in Cards app baked into iOS 5. (It's $2.99 for domestic delivery and $4.99 for international delivery with Apple.) Even better, this completely free app is available for both iOS and Android phones.