I have the same problem, but I can add a few comments:
Julia: with 12.04 I've been able to make the modem work two or three times (completely random)
When plugging the modem many times the system freezes but not allways.
From time to time, the modem is recognized after several minutes of being connected.
Most of the times, after plugging the modem, modem-manager crashes and apport opens to send a bug report (I don't know how to link the report to this bug)
I have the same problem, but I can add a few comments:
Julia: with 12.04 I've been able to make the modem work two or three times (completely random)
When plugging the modem many times the system freezes but not allways.
From time to time, the modem is recognized after several minutes of being connected.
Most of the times, after plugging the modem, modem-manager crashes and apport opens to send a bug report (I don't know how to link the report to this bug)
None of that happened with 10.04.