GSM is a robust mobile network on which cellular operators worldwide transfer voice signal from a cell tower to your mobile phone. All mobile devices even of older generation support GSM standard which allows you to make phone calls. GSM standard works on 900 MHz frequency. It’s suited for propagating both through urban and rural areas.
EGSM is an advanced GSM standard extended for additional 10 MHz. It works on the same 900 MHz frequency. Currently, all mobile operators switched to this voice network and support both EGSM and GSM.