Having an Eye-Fi wireless SD card in your camera is useful, but only if there's a wireless network to connect to. Soon, though, anyone with an Eye-Fi X2 will be able to upload photos through their phone's 3G connection.
Here's how it works: The Eye-Fi sets up a little ad-hoc network; the smartphone app connects to it; pictures are transfered to the smartphone; pictures are uploaded to anywhere and everywhere, via the phone's connection. It's pretty quick:
It's a simple concept that probably wasn't too difficult to pull off, but the effect is totally transformative. With this app, every photo you take with any Eye-Fi-equipped camera can be uploaded as long as your phone has an active data connection. Your DSLR is a cellphone camera, now.
The Android and iPhone apps are due later this year (Eye-Fi couldn't get more specific than that) and will be a free update.