A couple of threads at Ubuntu discuss 10.04 and the iPhone 4.
http://ubuntuforums....&highlight=iphone
http://art.ubuntufor...ead.php?t=1516700
It doesn't look too good at the moment - iOS4 seems to have some format changes or something.
[edit:] One of the replies mentions using a virtual machine to run iTunes. Maybe that'll let you get it going until there's a reliable native Linux solution.
Good luck.
Cheers,
Scott.