I have never heard of AT&T sending salespeople door-to-door. Never. And both my parents worked for Ma Bell ... my father for over 40 years.
Your house needs some kind of security at the front door. Those chains that allow the door to open 6 inches are a start, but they only work if the person outside doesn't kick the door. Better would be a two-way intercom, so your wife can speak without opening the door, and without even being seen.
IMHO you and your wife need to have a discussion about home safety. If she's home alone (or with kids, then kids arrive), she should NOT open the door to strangers. In today's world of laser printers and digital photos, NO ID is worth the plastic it's printed on. Anyone can make an official-looking ID. "We're not interested," is a perfectly acceptable reply to any question. After all, if you want something AT&T offers, it's not like you can't pick up the phone, log onto the Internet, or visit an AT&T storefront on any main street or in any shopping mall.
With respect, both you and your wife messed up. She should have closed and locked the door immediately. Her FIRST phone call should have been to the police. Anyone who will not leave when told to leave is trespassing ... period. That's a police matter. She should have called you AFTER she called the police, to let you know the police were on the way. At that point, you could have told her to get the gun ... and at that point she should have gotten the gun.