Dallas is a huge cultural shift from Chicago. Make very sure you want to live there before relocating for a company like this.
The weather is HOT 9 months of the year. Most people never go outside because it's so miserable. If you like green grass, occasional rain and winters, you will hate Texas.
Dallas is a huge step down in terms of culture vs Chicago. the Dallas Fort Worth Metroplex is an endless sprawl of highways, traffic and ugly neighborhoods. The opposite of a high density urban metropolis like Chicago.
The people of Texas are nice enough, but you may not like their politics being from the north. AT&T management here, however, are extremely arrogant and demanding, worse than in other places.