I have a ZTE MF 636 and it is pretty much the same modem. The modem works as a USB-CDROM when you plugged it. You have to move to the modem side of the hardware. Older version used usbmodeswitch, but lately was recognised directly.
It was working nicely at the begining of Fedora 12 cycle, then it came one update, not sure if was from udev rules, kernel or what. People tend to blame NetworkManager, when the problem comes from hardware recognition.
You can look this bug ticket
that may help.
Right now my modem is working in Fedora 13.
1.- Boot the PC
2.- Plug the modem
3.- Wait until you have an icon on your desktop usually is from the Cell company.
4.- Used right click on the icon to get the context menu to eject.
5.- Wait a long time... really about two minutes or three minutes.
6.- when is ready it will show up an option on NetworkManager.
(I keep left clicking on network manager to check when is ready)
7.- Follow networkmanager instructions on setting up a new a mobile broad band connection.
There was one thing on Fedora 12 that sometimes the connection died after set up. You have to unplug the modem and start over, but this time you skip the broad band connection set up, as NetworkManager remember what you did before. I haven' t seen that problem on Fedora 13.
Hope it helps.