I had this problem, which meant my iPhone no longer automatically mounted in Ubuntu 10.10. I had recently upgraded the iOS to 4.3.1 and this turned out to be the cause of the issue.

So, to fix it:

1. Click on the System menu, then Administration and Software Sources. You’ll have to enter you administrator password.
2. The Software Sources window will open.
3. Click on the Other Software tab and click on the Add… button.
4. Enter the following into the APT line box:
5. ppa:pmcenery/ppa
6. Press “Add Source”
7. Then click “Close” And then “Reload” on the next question.
8. Click back on the System menu. then Administration and finally Synaptic Package Manager.
9. Once the window has loaded, click into the search box, and search for:
10. libimobiledevice1
11. The program may tell you that it will need to uninstall libimobiledevice0 and upgrade some other thing. I said OK to all this and then press Apply.
12. It will run through, download the new modules and install them.
13. Restart your computer for these changes to take effect.