Comment 9 for bug 1014054

Phillip, it looks like your SIM card is the issue. So until the bug can be fixed in the package you can workaround it a couple ways. SIM cards actually have versions as well; try and see if you can get a different SIM card that does work with your modem or grab and install the version of modem-manager for 11.04.

http://packages.ubuntu.com/natty/modemmanager

Next, I would add the additional information you found out to your bug report and assign this bug to the modemmanager package in launchpad. Then, work with those developers to help get a permanent fix for your issue. Good work on debugging!