Three of the UK's largest mobile phone companies took at least five years to tell customers their voicemails had been hacked, the Leveson Inquiry has heard.
Vodafone, Orange and T-Mobile established that 156 people on their networks were hacking victims after News of the World royal editor Clive Goodman was arrested in August 2006.
But fears about prejudicing the police investigation meant Orange and T-Mobile did not notify those affected until last July - and Vodafone told victims only last month.
By contrast, O2 said it discovered that about 40 of its customers could have had their voicemails illegally intercepted and contacted them five years ago, at the time of the original Scotland Yard inquiry.
The press standards inquiry heard that investigations established there were 40 hacking victims on the Vodafone network, 45 on Orange and 71 on T-Mobile.
Goodman was jailed along with private investigator Glenn Mulcaire in January 2007 after they admitted intercepting voicemail messages left on royal aides' phones.