The iPhone is capable of downloading ePub files and launching them in the reader of your choice now. For those of us who prefer iBooks to Stanza, why don't you provide a simple download link containing the ePub file instead of a stanza:// link. That way users can choose which reader's library to load it up in.
Help get this topic noticed by sharing it on Twitter, Facebook, or email.
Thanks for writing in with your suggestion. We'll certainly consider making the process smoother given the recent epub handling capabilities of the iPhone and iPad.
I would like to point out that while there is a 'View in Stanza' link in the mobile version at the bottom of each page, a bit further down is a link to 'Download this book'. This link will send the ePub file to your device and trigger the device's capability to choose your reading environment.