Milly Dowler's mother felt "euphoria" when she finally got through to her missing daughter's voicemail after a private detective deleted some of the messages, the Leveson Inquiry heard today.
Sally Dowler's hopes were falsely raised when News of the World investigator Glenn Mulcaire erased a number of the 13-year-old schoolgirl's voicemails, the Leveson Inquiry was told.
David Sherborne, counsel for the Dowler family and 48 other alleged victims of press intrusion, said: "Perhaps there are no words which can adequately describe how despicable this act was."
The Dowlers, who will be the first witnesses to give evidence to the inquiry, suspect that their own phones were also hacked, the hearing was told.
Sherborne said the Dowler family were also subjected to "terrible intrusion" when they retraced the route Milly was walking in Walton-on-Thames, Surrey, when she was abducted in March 2002.
The lawyer said they intended this as a "private moment" which would help them to come to terms with their daughter's disappearance.
But they were photographed and their picture appeared in the News of the World under the headline The Longest Walk.
Sherborne said Mulcaire committed an act of "cruelty and insensitivity" in hacking Milly's phone.
He said: "Mr Mulcaire, acting in the course of his work for the newspaper, had deliberately accessed and listened to the missing 13-year-old's voicemail.
"And worse still, he had even deleted some to ensure that there was room for waiting voicemails to come through to their otherwise full mailbox."
He went on: "Mr and Mrs Dowler will tell you in their own words what it felt like in those moments when Sally, her mother, finally got through to her daughter's voicemail after persistent attempts had failed because the box was full, and the euphoria which this belief created, false as it was unfortunately.
"Perhaps there are no words which can adequately describe how despicable this act was."
Mulcaire was jailed with the News of the World's former royal editor Clive Goodman in January 2007 after they admitted intercepting voicemail messages left on phones belonging to royal aides.