Copy this script into the AppleScript editor, and save to a location on your harddrive.
tell application "iTunes"
repeat with s in sources
if (kind of s is iPod) then update s
end repeat
end tell
Next step is to download and install Lingon and setup a launchd configuration to schedule your nightly iPhone sync. Here are the settings I used:
Save your launchd configuration, logout and log back in - and enjoy!