By Martin HickmanNews International staff or contractors made more than 6,000 calls to voicemail inboxes before police smashed the phone hacking operation at the News of the World, the phone hacking trial heard today.In a two-year period leading up to the arrests of NoW reporter Clive Goodman and the private detective Glenn Mulcaire in August 2006, they and journalists at News International made 6,813 calls to 281 unique voicemail numbers, or UVNs.Calls to UVNs have been described at the Old Bailey as "hacking calls" - attempted or successful interceptions of mobile phone messages.A phone data specialist at the Met's hacking inquiry, Operation Weeting, Detective Constable Steven Fitzgerald, disclosed the data to the trial.He explained the police had call data for four types of phone; News International's ordinary hub system; NI's 'private wire' [a Vodafone mobile number shared by several staff]; landlines at Mulcaire's office in south London; and the landline at Goodman's home in south London.He said the billing information for News International's hub between July 2004 and August 2006 was supplied to the Met by News International, while the 'private wire' for October 2005 to August 2006 came from News Corp's Management and Standards Committee.Det Const Fitzgerald told the court there were a total of 4,714 calls from NI's hub and 'private wire', to 135 voicemail inboxes.Police were able to recover call data for Mulcaire's landlines covering February and April 2005 and December 2005 and August 2006. There were 1,450 calls to 132 UVNs, Det Const Fitzgerald saidFor Goodman's home between January 2005 and August 2006, there were 649 calls to 14 voicemail numbers.Detective Constable Fitzgerald said that the police had only been able to track calls to UVNs they knew, meaning that there was "every possibility" that the number of calls to voicemails was higher.Addressing the jury, Judge John Saunders told the jury that the prosecution case would end tomorrow. He added that the current timetable suggested that at the latest (the "worst case scenario”) they would retire to consider their verdicts in mid-May.He told them that them it was important they continued to approach their task diligently, saying: "It's an important case for the defendants, for the public, for everybody."All the defendants deny the charges, which include conspiring to hack voicemails and conspiracy to pervert the course of justice. The case continues.