BSNL yes indias one of the biggest network.It was well known for its low speed.But recently after jios release, BSNL announced new cheap internet offers which were far ahead than the other operators including jio.But, when you get 3 gb data a day and you are suffering to use atleast I gb out of it due to low speed the network sucks for you doesnt it? The main issue with BSNL is low stability and reliability.The speed keeps varying most of the time and sometimes even at full range, you dont get internet.This may not be the scenario with all cases, but most of my friends agree to this.So, you have to make a choice.Do you want to hold on to a mobile network that doesn even give 4g and with no stability just because it is cheap and gives a lot of data?