BT Phonecards were used in Britain's prisons from the late eighties to the early noughties. These specially encoded cards normally carrying the wording 'For Use in HM Prisons Only', couldn't be used in public cardphones.
Prison use only - last ever optical BT Phonecard produced by Landis and Gyr in Swizterland in 2003? The front and reverse of the card is shown. The card is produced on thin plastic and has a control number prefix of 309C.