iPhone 3G bluetooth unaccessible
Without a jailbreak, iPhone Bluetooth only supports headsets and wireless tethering.  Developers can also use the Bluetooth API to allow apps to communicate but this has limited functionality.  So basically your iPhone won't discover your phone, laptop (unless it's a MacBook) or desktop because it's not designed to do so.  With the MacBook, it appears that the only functionality allowed is data tethering and no file transfers or other features are enabled.