The free application lets you print photos wirelessly to any local networked HP Photosmart printer from an iPhone or iPod Touch. It is limited to 4" by 6" prints, and will automatically choose the appropriate tray if your printer has a dedicated photo paper slot`.
iPrint’s interface is simple. It lets you browse all of the installed photos on your iPhone. Selecting one displays a Print button, which sends the image directly to the printer when pressed. There aren’t any extra options, other than a “chooser” for multiple printers. I downloaded the program from the iTunes App Store, and, upon launch it instantly found the Photosmart C7280 on my network, and printed borderless photos without any hiccups.
All-in-all, a pretty slick implementation/proof of concept. And, while iPrint Photo is limited—at least for now—to photos, you can use the iPhone’s built-in screen capture feature in a pinch if you want to print a map, email or other iPhone data.