iBerry is a OWA proxy application that runs on the iPhone and can convert your OWA mails to POP and then into Mail. Its still in an early stage of development but it is functional. http://streampodder.com/iBerry/
Its only a web scraper so there is nothing to be worried about. It will either work or not work at all. And it will not delete any mail from your outlook so its all very safe. If this project does not work for you then you could check http://www.hackint0sh.org/forum/showthread.php?t=3023 which is another porject along the same lines but its a little further along in development. I have to try and do some ObjC and UIKit to create a config screen and installer for my app so thats what i am working on at the moment.