What makes the police think the driver was on the cell phone? They're not going to ask for the records just on a whim.
And the phone records would then be compared against the car's black box. Newer cars' computers are going to show exactly when the air bags deployed. Some will actually show the speed. What you're looking for is cross-referencing the two. The fact that someone was on the cell ten minutes before the accident is not important, and even a minute before the accident isn't too important (in 60 seconds, at 30 mph the car will travel one half mile). Now if he disconnected ten seconds before the accident, yeah, he was probably distracted.
The state's cell phone law would determine whether the driver was reckless, in that violation of a travel ordinance that results in an accident is considered evidence of reckless behavior. For example, same accident description on a road where the speed limit is 30 mph. First driver is going the speed limit, second driver is going 40 mph. The speed is evidence that the second driver was acting recklessly. (I'm being very simplistic here.)
Best of luck,
Jim Clark-Dawe