What about the new 3.0 software for the iPhone?
http://developer.apple.com/iphone/program/sdk/
This is exactly what you are looking to do:
http://developer.apple.com/iphone/pr...cessories.html
or a version of this:
http://developer.apple.com/iphone/pr...eertopeer.html
I love my iPhone and it would be so awesome to have a Castle Link app. I really dont think that it would be that hard to do. Just comeup with a usb accessory and make the software free. I would have to bet the accessory could sell for $20.
By the way. We use exchange on our server and looked into blackberrys, windows moblie, and iPhone. iPhone works the best. Blackberry wants thousands of $$$ to work correctly with exchange. iPhone works right out of the box.