Comment 7 for bug 311581

This bug was reported against Jaunty, about what I understand was pure dial-up modems, not 3G modems. Assuming the same concepts apply to NM 0.8 and later doesn't work unfortunately.

If you're still having an issue with 3G modems, please test in Lucid or the development release (Maverick), and open a new bug specific to your hardware, and report the bug number here. Please make sure to report bugs that include standard information such as described in https://wiki.ubuntu.com/DebuggingNetworkManager or use the 'ubuntu-bug network-manager' command.

For those with standard dial-up modems (*not 3G*), as a workaround you might be able to set the device in /etc/network/interfaces and use pre-up etc. scripts to make it work. NetworkManager will just ignore devices set in /etc/network/interfaces and assume they are UP.