How to display UMTS signal strength?
modem-manager-gui gives that info on "info" tab:
In distros other than Ubuntu, the package name can be modem-manager.
Since version 0.8.1 of network-manager is already all-inclusive (http://live.gnome.org/NetworkManager/ReleaseProcess).
Otherwise you can use umtsmon (http://umtsmon.sourceforge.net/)
or vodafoneMobileConnect (https://forge.betavine.net/projects/vodafonemobilec/)
or bcm (https://forge.betavine.net/projects/bcm/)
if you have a too old version of ubuntu that does not allow you to update network-manager.