"The inquiry is near completion and the challan (registration) will be filed soon," the chief minister told reporters here.
He said certain telephones were illegally tapped during the previous Bharatiya Janata Party regime.
Singh, however, hinted that some officials had vested interests behind recording the conversations.
"Some of the officers were recording conversations not for their entertainment," he said.
The present Congress government, which is completing a year of its formation Wednesday, has accused the Prem Kumar Dhumal-led previous BJP government of tapping telephones illegally through the state criminal investigation and vigilance departments.
Dhumal, however, has refuted the charges.
The total number of phones tapped, mainly of Congress leaders, government functionaries and journalists in violation of the Indian Telegraph Act, was over 1,300, officials said.
The vigilance and anti-corruption bureau in June lodged a first information report (FIR) in the case. But so far no one has been named in the FIR.
On the issue of a probe against Aam Aadmi Party leader and lawyer Prashant Bhushan's Kumud Bhushan Educational Society, named after his mother, that was allowed by the previous BJP government to purchase 4.68 hectares of land in a tea plantation, the chief minister said "he (Bhushan) is not above the law".
"Mere inquiry doesn't mean that someone is guilty. Independent investigation is going on into the purchase of a tea garden by Bhushan. If he is found guilty, action will be taken against him. He is a citizen of India and not above the law."
The chief minister said Bhushan had purchased the tea garden at Kandbari in Palampur in the name of the society, which legally he could not purchase as there was a total ban on selling tea gardens in the state to non-agriculturists.