BenQ S660C - Manual (Page 21)

Preparing Your Phone For Use 7
strength and the name of the network operator. You can now
use the phone.
8
If the phone cannot detect the network, the on-screen signal strength
meter will show no bars.
8
If the phone links to a network that you are not authorized to use, the
signal strength meter will show a level of zero. You will only be able to
make emergency calls.