LuEllen Robertson testified as a custodian of records for AirTouch Cellular, the mobile phone provider whose records were used to establish call activity relevant to the case. Called by the prosecution and examined by Marcia Clark, she explained the types of cellular phones her company serviced — portable, transportable, and car-installed — and the limitations of what their billing records could and could not reveal about how a phone was being used. Johnnie Cochran cross-examined her the same day.