I got the information below from various places. I haven't tested it, since I don't have the modem or the broadband service.
You might have to switch your modem into the "serial" mode of operation. It probably defaults to the "storage" mode.
Create the file "/etc/usb_modeswitch.conf" containing the following.
Use the following commands (from a "root" shell) to switch the modem into the serial mode. You will have to do this every time that you connect the modem. You might want to add the commands to the startup scripts.
You should now have a "/dev/ttyUSB0" device. The verify that, use this command.
Now you should be able to use the network manager to set up "/dev/ttyUSB0".
Make sure that you have set the executable permission on "/etc/rc.d/rc.networkmanager" in order for it to start.
chmod +x /etc/rc.d/rc.networkmanager
In the network manager you need the following settings.
Phone Number: *99#
Authentication: Allowed Methods: PAP
Allow BSD Data Compression: Yes
Allow Deflate Data Compression: Yes
Use TCP Header Compression: Yes