I have a Sierra Wireless 320U USB-to-WWAN modem that does not work with the current sierra and sierra_net drivers included in the Linux kernel. The manufacturer has an updated driver available from their website at http://mycusthelp.net/SIERRAWIRELESS/_cs/AnswerDetail.aspx?aid=44. My modem device works after installing this updated driver. I tested using the current Ubuntu-precise development release with kernel 3.2.0-17-generic from the Ubuntu repository and also the mainline kernel release 3.3.0-030300rc5-generic from http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.3-rc5-precise/. The direct link to the updated driver is at http://www.sierrawireless.com/resources/support/drivers/linux/v3.2_1740_kernel-3.0.directIP.tar. Sorry if this is filed under the wrong component, but I wasn't sure whether it should be under USB or Network.
All USB bugs should be sent to the linux-usb@vger.kernel.org mailing list, and not entered into bugzilla. Please bring this issue up there, if it is still a problem in the latest kernel release.