[itimpi]

Calibre can only "see" devices that look like a USB disk when connected. Apple prohibit any software other than iTunes from using the USB link to transfer files so Calibre cannot transfer files to iPhone like it does to other ereader devices.

What eReader software are you using on the iPhone? If you are using something like Stanza then the approach is to activate the Calibre Content Server (under the Calibre Preferences). You can then tell Stanza that Calibre is a book source and connect to it (via WiFi or 3G) from the iPhone end.

If you are using other eReader software then the Calibre Content server can be accessed either as web pages or as an OPDS compatible catalog. So as long as the eReader software can support one of those it can get files via the Calibre Content Server..