Comment 11 for bug 469881

I can confirm that the workaround of removing the modemmanager package does the trick for me, allowing me to use my USRobotics USR5637 dialup USB modem with gnome-ppp without problems in Karmic. I did not have to "completely remove" the package in Synaptic, only doing a regular package removal. This workaround probably leaves my system unable to talk to wireless 3G modems, but that is not an issue I can test or need to face.