By Steve Lohr, The New York Times Company Melissa Brinkman’s troubles are threatening to slow down AT&T’s multibillion-dollar rollout of ultrafast 5G wireless technology. Brinkman is CEO of Custom Alarm, a company that installs and monitors home and commercial security systems, fire detectors and personal emergency alert devices in and around Rochester, Minnesota. Those alarm devices were mostly designed to communicate using slower 3G wireless technology.