After two weeks of restless work I could manage to develop Mac OS X device driver and firmware loader for vendor specific usb device (Qualcomm Gobi Mobile Broadband device).
qcserial USB driver for linux directed me to the right direction. First of all, I was trying to upload firmware to the USB device after making some changes to SimpleUSBNotification example shipped with XCode. I had to port the codes of for Mac OS X.
Though I could upload the firmware after few days of work the device were not working as I expected. Because, the device and all its interfaces (class, subclass, protocol) were defined as vendor-specific. As a result none of the existing usb modem driver were recognizing it.
Then I was planning to develop a driver for this. My target was to expose a vendor-specific USB Interface (Interface #2) of the Composite USB device to be exposed as a port under /dev/tty.* using the driver and then use that port to connect dial-up internet.
Then I found a usb modem driver called AirPrime. I have been trying to modify this driver so that the modified source codes work for my usb device. And finally the success came to me. I could load the driver during boot which do recognize my usb device after uploading the firmware and then I can connect internet without any problem
Please let me know if you want me to upload the modified source codes. Thanks for your time.
rubel's blog 
shm7478 said
Im very interested into this solution because I’m looking since I got my aoa150x-g3 about 1 year ago. So please make a howto for it.
Rubel Ahammad said
Could you please explain us what is ‘aoa150x-g3’? And how does this relates to this driver for Qalcomm Gobi Mobile Broadband device?
jerryzhow said
Well done.Rubel. I need the modified source codes. Could you send it to me?
THANKS A LOT. xinany@gmail.com
Rubel Ahammad said
Dear jerryzhow,
Thanks for your interest. Please find the source codes here. I am sending you the files as it was in my development folder. You need to copy and paste the firmware image files (amss.mbn and apps.mbn) in the folder ‘0’ to run the application.
You may need the code less kext that I am using for the modem.
Rubel
Ian McFaul said
I know this thread is a bit older now, but I’m wondering if you’ve considered building/posting a final, completed kext?
Lots of folks who have Google’s Cr-48 prototype Chrome OS notebooks and have loaded Mac OS X on them would love to have this working to use Verizon’s broadband in OS X as well as Chrome OS.
Rubel Ahammad said
kext for the modem is available and you can download it from the link I have given in my previous answer. But we need a firmware uploader to make this device behave like a modem. I am working on this. I will soon share the firmware uploader with you guys soon.
Thanks for your interest.
Rubel