Russian prisoners can communicate with fsin-pismo, a mailing app for iOS, Android

The mobile application, called "fsin-pismo", operates on the iOS and Android platforms and can be used to send messages to an inmate at a particular prison or correction facility.

The prison will check and censor the message and then hand a printout to the inmate in question, said Alexander Polkin, deputy chief of Moscow's SIZO-5 Pretrial Detention Center.

The application can also be used to send photos.

A similar service for emails has been provided since 2008.

The service is unique and has no counterpart anywhere in the world, Polkin said.

After it has been tested in St. Petersburg's Kresty pre-trial detention centre and Moscow's SIZO-5, it will be introduced in all prisons and correction facilities throughout the country, he added.

It will cost 30 rubles ($1) to send a message to an inmate from a smartphone.

At least 100 emails arrive at SIZO-5 each day, a third of which are sent from mobile phones, Polkin said.