Many manufacturers make modem based on Huawei data card including well known brand. This bring possibilities of generic driver use provided by Huawei but mostly manufacturer may specifically use particular version (maybe their hardware don't posses feature in newer driver?)
I had VT-12 CDMA usb modem for 3 years now on XP and seems a bit working in Mac too. Now it bugged me when I plugged this on Server 64bit (Win 2003) machine and can't install. I tried to find on manufacturer's site but there is no update (gone actually) and their last vista64 driver isn't signed. Time to check the main vendor!
1. Go to http://www.huaweidevice.com/worldwide/downloadCenter.do?method=index
2. Search for "UTPS" (driver package name)
3. Download latest date Driver for Windows
4. Open with 7zip then rip off (open inside) the zip file, then exe file till you get "common" folder, inside it extract "driver" folder.
5. There is your drivers! for VT-12 we only need serial (ewser2k) and modem (ewusbmdm) files. For Windows 2003/XP 64-bit use the Vista64 version.
note: make sure you update both Huawei 3G modem and 3G Application Interface