Blockchain It works on my iPhone 4S. No jailbreak required, I got it from the App Store.

There were only two tricky parts:
 - the QR code you need to link to your blockchain.info account is under My Wallet> Account Settings > Devices on their website.
 - the Captcha image is very easy to read and type. Just ignore the little squiggles at the front of the ascii characters - only type what looks like letters/numbers.

I've already confirmed it allows money to pass into the wallet, and out. QR code functionality also work.

--V