Several people out there who use Ubuntu, also have iPhones. Ubuntu connects fine to an iPhone, unless you have recently performed an iPhone OS upgrade to 4.2 or 4.3. There is a PPA for this (thanks for the tip sn9). Here is how to get your iPhone connected again so Ubuntu recognizes it.
Open up a terminal and copy/paste these commands (press enter after each command):
sudo add-apt-repository ppa:pmcenery/ppa
sudo apt-get update
and do this one too:
sudo apt-get upgrade
This should fix the problem! Try plugging in your iPhone now and see if Ubuntu recognizes it. If not, try rebooting. If its still not fixed, continue with these final commands in a terminal window:
sudo apt-get install libimobiledevice-utils
and also these:
And that should do it!