I am using Samsung Galaxy S2. and MIUI (2.3.30).
I added a number from Call Log to black list. The number is added in the black list of AntiSpam. But don't know why it doesn't blocks the specified number.
I have this problem too. Sometimes 2 or 3 bars. Very occationally 4 bars. Problem since installed 2.3.23, upgraded to 2.3.30 but this signal bar seems to have some kind of problem, changed modem still no effect.