"GNUTLS ERROR: A TLS packet with unexpected length was received" when I connect my iPhone 3G

You don't have to jailbreak your Iphone with Ubuntu however you will probably have to add a new "PPA source" to your Ubuntu installation to get the required packages for Ubuntu to Recognise your phone.

The ppa you will need to add is ppa:pmcenery/ppa to add this open a Terminal from the accessories menu and type this at the prompt.

sudo add-apt-repository ppa:pmcenery/ppa

and hit enter once this has been added type this command in the same terminal

sudo apt-get update

and after

sudo apt-get upgrade

this should upgrade your package libimobiledevice to version 1.0.4 from 1.0.1 enabling you to access your Iphone

PPA Reference:

• What are PPAs and how do I use them?

edit

Having had a a good look around for Idevice mounting tutorials I found this at ubuntugeek it goes through the procedure of manually mounting the device including all of the required packages and file edits to get this to work hopefully this is the solution to your problem. Bearing in mind that the tutorial was written for Ubuntu 9.10 and for an Ipod touch there is a quote at the end of the tutorial

Update from our reader :- It works for Iphone 3g. But at the end of preparation procedure you need to restart both your computer and the iPhone device.

Edit 2

if you receive this error message when trying to mount with Ifuse

GNUTLS ERROR: A TLS packet with unexpected length was received

You need to pair the phone with your pc to do this enter this command

idevicepair unpair

Your Iphone or other Idevice will automatically try to re-pair. You can then unplug it and plug it back in and it should mount correctly.

The correct ppa is sudo add-apt-repository ppa:pmcenery/ppa as per the Launchpad page.

Try this and let us know how you get on.