Okay. I know how there are many that hate to hear comparisons from the Caylee Anthony case on this thread. But I was pretty well saturated with it for the last three years. I'm certainly no expert on all the cell phone threads, but IIRC, the only things that could be determined from the cell phone providers were the times and the pings (which indicated a general area of the cell phone.) This is very useful, of course, if you know who is in possession of the cell phone, to determine who was contacting whom.
It played out that LE was very pleased that Amy H (one of Casey's friends) had a plethora of texts that she had not deleted from her phone (all documented and available in the Caylee forum). Casey's mother seemed to have deleted hers and they were not available for the investigation. This leads me to believe that carriers do not have access to content of text messages. There were also a couple of pictures found on a couple of ancillary players' phones. These were accessed through the cell phones, themselves. The text messages did register as activity on the carriier"s records but LE needed the phones to actually see what they were.
From the history of that, it makes me wonder if the last recorded activity picked up by the carrier (Verizon?) could have been a text message rather than a voice call. (IIRC, there was an indication on the carrier's documentation that distinguished between text and voice ~ Hope I'm remembering this part right ~ but would have to be checked out if we ever get to see the records.)
It also explains why LE (and everyone else) is eager to get the phones physically in their possession. There could be texts or photos that would be helpful and IMO that's enough reason for them to consider the cell phones important.