When connecting to mobile broadband the username and password are usually something standard. It will depend on you mobile network. This page may help http://www.quickim.com/support/gprs-settings.html
If you do want to avoid NetworkManager, then this guide I wrote may help http://www.trigpoint.me.uk/3GModemConfig
I would however second ozjd comments and try to get it working with NetworkManager, try a Fedora 11 live CD or USB to get back to defaults. Faulty settings can get stuck, as I found when I tried my brother in laws vodafone dongle in place of my T-Mobile N95.
Getting Mobile Broadband to work for me has always been.
1. Connect device and allow NetworkManager to detect it.
2. Attempt to connect, it will fail, but will will create the connection to edit.
3. Edit the connection, I have only ever needed Number, Username, Password and APN.