In order to acquire the first SIM card, you need to go to The Amusement Mile, i.e. into the North-Eastern part of Arkham. Your destination is a quite large balcony of one of the bigger buildings. You will bump into some bandits here. Attack the enemy from above and start a more regular form of fighting, which should cause no problems to you (use the cape on the best armored enemy).
After the fighting ends, locate the radio, which has been left in the location presented in the above screenshot. Interact with it to acquire the SIM Card, and use the Cryptographic Sequencer again. Just like before, you need to put the crosshair inside the orange circle and decipher the transmission then.