There actually is a full OED, unless it's missing something I'm not aware of:
http://itunes.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=307233030&mt=8
If the link doesn't work search for Oxford Deluxe by Enfour (it's £33). The reviews on the US iTunes store are better btw...not sure what's up with that.
It's not the OED. It's the Oxford Concise Dictionary or something similar to it - clearly they are hoping people like you will buy it thinking it is the full OED. In their defence, they do say say "Oxford's largest single-volume English Dictionary" in the first paragraph of the review.
I'm tempted by it, but I'd like to save my money for the full OED.