I been using bsnl sim card over 2 years and I have so much exoerience about thia company. It comes with onlg 3g support now days they worked hard to get 4G bands india but they are won upto give the 4G sims only in popular regions not everyone able to use 4G bsnl sims.
There quality of voice calls is not HD region wise it depends. Some time there is most difficulty in travelling the internet of bsnl is not working as well as most of the time the range of bsnl goes to 0 . In some serious times they are useless. The bsnl landline phones are comes with good quality and low cost .most of gov offices use bsnl internet. CUSTOMER SERVICE OF bsnl is worst most of time they are not answering our calls