Make sure to stress in your resume any sales experience. Answer the screening questions as if you were the most diligent ambitious and righteous angel, seriously. Just make sure you are consistent with the persona your build since they rephrase the same question several times to trip you up.
The final interviewer will take notes on your answers. Try to charm the interviewer early on so that he/she fills your answer sheet most favorably. Be patient and give your interviewer the time to write in your answers. The interviewer is not the final decision maker, however. The interviewer sends your answers to HR and they decide.
The purpose would be to touch on key points during the interview that illuminate yourself in a light that they find desirable. Using professional examples, prove you have traits such as sales skills or integrity, to name a few. Make them up if you have to, just make sure you would believe them yourself, and you can deliver these stories without flinching at your own lies. This is what sales is sometimes about.
Study the AT&T call flow, use that during the sales simulation. First greeting, then the building empathy and report using something personal. After that you tackle the problem given in the simulation simply by saying you will have whatever appropriate department handle the issue, use whatever information available then to offer a service solving or related to the issue. It is important to mention "bundling services" will save money. The interviewer will likely object, then you make a counter, offering something a little cheaper. Whether they accept or decline or if you're frisky enough to offer something else, you finish off by asking if there is anything else you can help with. Then say thank you, have a swell day.
Chit chat with the interviewer in the elevator and down the hall, but realize you're still being judged.
Be a person that the interviewer would like to have as an employee of his, while not upstaging or being pretentious giving your examples. Find that balance, and you have mastered sales and office politics.