The incident took place at the Tura district jail yesterday when a visitor Tengsrang Marak brought with him food packets for one Bansang M Marak, district deputy commissioner Pravin Bakshi said.
Jail authorities detected the handset hidden under the cake, which was meant to be handed over to another prisoner under trial William Sangma, a militant, he said.
During routine check and scanning of food packets, the mobile handset was detected and an FIR has been lodged in this regard.