You are making a major mistake in your thinking.
All signal meters are not calibrated to the same value (Bars/db)

A CDMA phone with two bars is not receiving the same signal as a GSM
phone that shows two bars.

One GSM phone with two bars is not receiving the same signal as another
GSM phone with two bars.

The threshold in db that a GSM phone will probably be the same
for many different phones, but the different phones may show a
wide range of signal levels (bars) for that minimum signal.

On the phone you have, the minimum signal that the phone will work
is equal to two bars on it's meter.
Other GSM phones may only show one bar, or possibly no bars if
it is calibrated to show no bars with the minimum useable signal.

I have one TDMA phone that will no longer work when the last
bar goes out on the signal meter,
and I have another one that will work at signal levels way below
the point that the last bar disappears.
But both phone will work (and/or) not work in the same locations.
Both phones have close to the same minimum signal capability.

And there is one phone I have around hear that wont read
under two bars even with the antenna disconnected.
And it won't work with less than 3 bars.