A few months back I made a python script available which monitored the Dell 5530 / Ericsson f3507g mobile broadband modem in Linux providing network, access type and signal information to a file for other programs (such as Conky) to pick up and display the data.
I've since updated this program to now use PyGTK to display a status icon indicating the signal strength and the access type. Through this icon the radio state can be changed to enforce 3G only, GPRS only or 3G preferred connections (aswell as turning the radio off).
The script should work in tandem to network-manager so you can still get online using something you already use. The only addition is a new status icon with your signal strength - something ModemManager should resolve when it becomes available as standard in a few months time. If you can't wait that long and want signal monitoring, then this is for you!
Additionally, if you use vnstat to monitor your bandwidth, clicking the status icon will display your current months usage for ppp0.
Dell 5530 / Ericsson f3507g 3G Signal Monitor for Linux
Update: Now lives on GitHub at https://github.com/bazwilliams/dell5530mon
Hopefully someone may find this program useful! If you do, why not consider donating to Multiple Sclerosis? There is a sponsorship button on the front page of my blog or at JustGiving