Prolink PHS300 redux

I’m using the Prolink PHS300 HSPA 3.5G dongle as my regular mobile broadband device.
It works perfectly on Ubuntu 11.04 with the high-speed option.ko serial driver.

(Some udev magic may be needed so that the serial port is correctly identified.

One oddity: when the device is plugged in and NetworkManager is probing the modem there are two brief periods (lasting 5 secs each) where the system (UI freezes, no mouse movement) is unresponsive. The system recovers quickly. Too weird for words.

This occurs in Fedora 15, Ubuntu 10.10 and Ubuntu 11.04.