Inmates have devised an innovative way to smuggle in cell phones into a prison farm in Brazil: carrier pigeons.Guards at the Danilio Pinheiro prison near the southeastern city of Sorocaba noticed a pigeon resting on an electric wire with a small cloth bag tied to one of its legs last week.

"The guards nabbed the bird after luring it down with some food and discovered components of a small cell phone inside the bag," police investigator Celso Soramiglio said Tuesday.

One day later, another pigeon was spotted dragging a similar bag inside the prison's exercise yard. Inside the bag was the cell phone's charger, Soramiglio said.

The birds were apparently bred and raised inside the prison, smuggled out, outfitted with the cell phone parts and then released to fly back.

"Pigeons instinctively fly back home, always," the investigator said.

Soramiglio said that police have not discovered who raised the pigeons nor the name of the inmate who was going to receive the cell phone, but that he hoped the telephone carrier would provide the information.

"Some of them are members of organized crime groups that use cell phones to talk to family and friends and to give and receive orders for criminal actions outside and inside prisons," Soramiglio said

police stopped a car as part of a routine check. In the boot of the vehicle they found the one-metre long model helicopter with a basket-like container attached to its base. Inside were nine mobile phones wrapped in a disposable nappy, while another five phones were also discovered in the vehicle.

Four suspects were arrested, and the youngest, who was aged just 17, is reported to have confessed they had been given $5,000 to buy and prepare the helicopter. They were apparently to be paid the same amount if they had successfully landed the model inside the prison walls.