If you want to eavesdrop on GSM phone conversations or data, it pays to have deep pockets, because you’re going to need to listen to a wide frequency range. Or, you can just use two cheap RTL-SDR ...

This project is designed to intercept and decode GSM frames using RTL-SDR, GNU Radio, and Wireshark. The GSM Sniffer allows you to capture real-time GSM signals, process them using GNU Radio ...