Indian police officials said that the terrorists who struck Mumbai in November were directed by people using Voice over Internet Protocol (VoIP) phone service, which complicated efforts to trace and intercept the calls. A month earlier, a draft United States Army report highlighted the interest of Islamic militants, such as the Taliban, in using VoIP.
To locate a VoIP caller, investigators need access to service provider databases that track the unique numerical identifier (I.P. address) of the device the subscriber uses to connect to the Internet. Additional work is then needed to locate the device, which can take days longer than a phone .
See, "Mumbai Terrorists Relied on New Technology for Attacks," New York Times, December 9, 2008, at http://www.nytimes.com/2008/12/09/world/asia/09mumbai.html?_r=1&scp=2&sq=mumbai&st=cse.