My experience with 3G modems, especially with Fedora 11 - 14:
If it was a Huawei modem, I could connect with the N
anager within 1 - 3 minutes without installing another program, if it was recognized immediately and shown in the NWM box.
Please first see, if the plugged modem is shown by Terminal:
lowercase "L" like list.
If not, unplug the modem, run in a Terminal
plug the modem and run "dmesg" again to see, if there are additional lines; if you don't see more output, it will be a problem.