We were Cingular customers, then AT&T bought them. It was the only wireless carrier that offered a good signal where we lived. Slowly over some time after that

We were Cingular customers, then AT&T bought them. It was the only wireless carrier that offered a good signal where we lived. Slowly over some time after that happened, the signal started to get worse and come and go like with the other carriers we tried previously. I'm not sure I'm trying to make a point, but I do not know what AT&T did with the Cingular. Did it use it's network? Did they just engulf it to remove the competition? Maybe someone else more knowledgable of this ordeal knows. How will AT&T use T-Mobile after they acquire them? What becomes of the T-Mobile network that will soon by AT&T's network?