Mind your SIMs

Johannesburg thieves have found a source of unlimited free calls for their cellphones - SIM cards inserted in traffic lights.
The Guardian says that about 600 high-tech lights in the city have SIM cards that alert authorities via GPRS to malfunctioning traffic lights. Thieves, apparently with inside information, have hit two-thirds of the lights (which look exactly like conventional lights), taking the SIM cards.
A spokesman for the Johannesburg Road Authority says, "They know which signals to target. They clearly have information." 
Since a repair costs $3,000, the South African city is discontinuing the program but conducting an internal investigation to find out how the SIM lights are being targeted.