A News of the World reporter told Surrey Police he was “100 percent certain” Milly Dolwer had travelled to Telford for work when she disappeared.
Ricky Sutton contacted Surrey Police’s head of communications Sarah McGregor while working on the story.
During the conversation, McGregor told Sutton that the message on the mobile had been addressed to “Nana” and not Amanda – Milly’s real name.
McGregor told the Old Bailey Sutton replied: “This is not true, it’s inconceivable. There’s other messages on her phone.”
Sutton said Dowler had travelled north after getting the job through the Mondays recruitment agency.
However, McGregor told the court the message on Dowler’s phone had been an error, due to someone entering the teenager’s number by mistake.
Officers investigating Dowler’s disappearance soon established the message had been intended for someone else registered at the agency.
Sutton maintained that his information was correct despite the denial. He told McGregor: "We know this for a fact, we are absolutely, 100% certain."
McGregor claimed she had been told by a colleague about Kuttner referring to the NoW having Milly's mobile phone number and pin when he called Surrey Police on 13 April.
But Jonathan Caplan QC, defending Kuttner, suggested she was mixing up two different phone calls – one from his client to her colleague where there was no mention of a pin number, and one where Thurlbeck told her the NoW was in possession of the pin number.
The barrister later asked McGregor: "When you were told on 13 April that Milly's voicemail had been accessed by News of the World, that did not cause you to refer it to anybody, that maybe this should be investigated?
McGregor replied: "I'm not a detective and I was not working as an investigating officer – it would be their decision."
All the defendants deny all the charges.
The trial continues.