I just installed ubuntu server 12.04. The server detects the modem, but I can't edit mobile broadband settings (to input username and password) in network connections
If you are asking how to do it-
As pointed out by @Eliah kagan,my answer points to a graphical way that may not be available in Server edition.And as suggested by him,I keep the answer intact with an addition of a possible useful link.
This link may help for the server edition- http://www.sourceguru.net/setting-up-networking-on-an-ubuntu-server/
While for a graphical way-
Under Ubuntu 14.04 it's all much easier, but there are still a couple of issues.
I'm in the UK. My mobile modem is a ZTE MF730M connected to the Three mobile network. I had to connect the device to a Windows machine and register it with Three before it would work. The first time you plug the modem in, it connects you to the Three website to allow you to register. Once you have done that, you can access other websites.
Next issue: the device includes a bit of data, which holds Windows drivers and windows config stuff. It looks to the host computer like a USB CD-ROM. When you connect it to your Ubuntu machine, it automounts the "CD", which disables the modem. To fix this:
to find out the mount point:
/dev/sr1 4354 4354 0 100% /media/simon/ZTEMODEM
So in my case that's
and the connection starts to work.
If I open the system settings tool and look at the network settings, there are now two "Wired" entries. One has two arrows next to it, one up, one down, and represents the connection through my mobile modem that has just been set up. The other has a picture next to it showing an RJ45 socket with the plug pulled out. That represents my real wired connection.