I take it that you didn't have the problem in windows. I use the u760
3g modem. Because the device has a memory device built in to install a
driver for windows, I must eject the memory device before the system
recognizes the modem. I have set up the network connection to auto
connect so should the reception be weak it will reconnect when the
connection fails.

I found the information on my modem on the Sprint network site, you may
look up your modem and determine it is supported with Linux on the
manufactures website.

The other option is to use a WiFi port, I have a friend that uses such a
device and then the OS is not important.