Started a Google search for "jonbenet Ramsey + phone records.
And first hit came up with something I've never heard of before:
"The Missing December Cell Phone Records
Discussion
This element of the case puzzles me. Steve Thomas goes on and on about how the DA's office denied subpoenas for Ramsey phone records, but after a year the police got a signed limited permission slip from John Ramsey to view his home and cell phone records between December 1 and December 27, 1996. The home phone records were unremarkable and the cell phone records were blank for the month of December. Thomas says Ramsey had the account since 1994 and prior months averaged 90-100 minutes of activity.
Here's the section from Thomas's book:
The Air Touch cell phone records were useless...December, the only period we were allowed to see, was empty. No calls at all. I asked if someone could remove billing records from the computer? "No way," the Air Touch source told me. "All these months preceding December are busy, and not one call was logged for that entire month?" The representative was firm: "There ain't no way anybody altered these records."
link to passage
Question: Can someone have altered the records? Edit for more questions: Is this the worst investigation in the history of crime that all phone records were not subpoenaed within the first few weeks? Does anyone know what this DA was afraid of?"
https://www.reddit.com/r/JonBenetRamsey/comments/axt887/the_missing_december_cell_phone_records/What are the chances of that that John made no cellphone calls in December!