"This was some employees' idle curiosity," a source at the company told the news network.
The source would not say how many of its workers were involved but said "we now consider this matter closed."
Verizon Wireless had notified the Obama transition team the company's employees accessed Obama's phone records.
Lowell McAdam, the Verizon chief executive officer, said Thursday that the cell phone involved in the security breach was a simple one, not a Blackberry. He said employees who looked at the records could have seen the telephone numbers of those calling or getting calls from that phone and whether voice mail messages were left, but they could not learn what was said.
He said all employees with access to the records were placed on leave after the breach was discovered. Those who have been fired were not authorized to look at them.
Verizon was still investigating whether any information was leaked outside the company.
During the 2008 presidential campaign, the State Department discovered that some contractors had been looking at passport files of presidential candidates and celebrities.