New MVNO That Uses Cingular's GSM Network

I recently took the TracFone GSM (Nokia 1100) into the supermarket down the road once again. When I took it to the back of the store, where it gradually lost the Cingular signal, it then used to change to "Roaming" and picked up the stronger signal from the ex-AT&T tower on the same road.

What the phone did this time, was gradually lose the Cingular signal, then had no service. Apparently, it did not pick up the ex-AT&T tower signal. Not exactly raising the bar.

Comparison:

T-Mobile: Full signal, all 7 bars (at 1900 MHz)
TracFone (Verizon): 5 bars out of 7
Cingular: What happened to the bar?