Unitech is owned by billionaire Ramesh Chandra whose son Sanjay is the public face of the group.

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For example, Wipro's revenue from its deal with Unitech Wireless, a mobile-phone company, depends on Unitech's subscriber growth.

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Unitech denied that the voice on the tape was that of Mr Chandra.

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On Wednesday, a court in Delhi rejected the bail applications of Swan Telecom Director Vinod Goenka and Unitech Wireless Managing Director Sanjay Chandra.

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News channel CNN-IBN broadcast what it said was a conversation between Mr Singh and Sanjay Chandra, the managing director of Unitech, a property company.

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Telenor, which holds a two thirds stake in Unitech Wireless, has asked that Sanjay Chandra step down as chairman of their telecom joint venture and that Unitech should appoint a replacement.

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