The dossier says handlers used a virtual phone number provided by service provider CallPhonex to call a cell phone used by one of the terrorists in Mumbai, according to printed reports.

"The controllers/handlers used the virtual number to contact a mobile telephone with one of the terrorists," the dossier says. 

"This conversation was and, thereafter, all calls made through the virtual number were also intercepted and recorded."

The dossier does not describe whether authorities the call via a tap on the wired portion of the network or by eavesdropping on the wireless leg of the connection.

CallPhonex could not be reached for comment.