"A highly sophisticated spying operation that tapped into the mobile phones of Greece's prime minister and other top government officials has highlighted weaknesses in telecommunications systems that still use decades-old computer code.
The spying case, where the calls of around 100 people using Vodafone’s network were secretly tapped, remains unsolved and is still being investigated. Also complicating the case are question marks over the suicide in March 2005 of a top engineer at Vodafone Group in Greece in charge of network planning."
There is also a detailed writup well worth reading. From that article
"The cellphone bugging began sometime during the fevered run-up to the August 2004 Olympic Games in Athens. It remained undetected until 24 January 2005, when one of Vodafone's telephone switches generated a sequence of error messages indicating that text messages originating from another cellphone operator had gone undelivered. The switch is a computer-controlled component of a phone network that connects two telephone lines to complete a telephone call. To diagnose the failures, which seemed highly unusual but reasonably innocuous at the time, Vodafone contacted the maker of the switches, the Swedish telecommunications equipment manufacturer Ericsson.
We now know that the illegally implanted software, which was eventually found in a total of four of Vodafone's Greek switches, created parallel streams of digitized voice for the tapped phone calls. One stream was the ordinary one, between the two calling parties. The other stream, an exact copy, was directed to other cellphones, allowing the tappers to listen in on the conversations on the cellphones, and probably also to record them. The software also routed location and other information about those phone calls to these shadow handsets via automated text messages."
Detailed writup: http://www.spectrum.ieee.org/jul07/5280
Article Link: http://www.techworld.com/security/news/index.cfm?newsID=9463&pagtype=samechan