Looks like BSNL enabled IPv6 in Telangana!

I can ping IPv6 addresses.

 ping6 -c 3 2001:4860:4860::8888
PING 2001:4860:4860::8888 (2001:4860:4860::8888) 56 data bytes
64 bytes from 2001:4860:4860::8888: icmp_seq=1 ttl=58 time=13.2 ms
64 bytes from 2001:4860:4860::8888: icmp_seq=2 ttl=58 time=13.3 ms
64 bytes from 2001:4860:4860::8888: icmp_seq=3 ttl=58 time=13.5 ms

--- 2001:4860:4860::8888 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 13.209/13.323/13.462/0.104 ms

Is this it? Or is there a catch?

Also, how can I make sure my internet connection defaults to IPv6?
You don't have to do anything, system and software will take care of it.
@pr0m3th3u5 Please advise:
@!!..PD..!! bro MH has IPv6 just not in all cities. It's already present in Mumbai and Pune. Not sure about other towns.

@Chip Thanks for the update. I have been getting the v6 address in ONT and Router for months now but pinging to ipv6 sites or doing any IPv6 test fails everytime.

Can you please share a screenshot with IPv6 ping test or IPv6 test working for you in Pune?
I use BSNL mostly for guests so dont have any laptop or computer connected there. Sorry, so no ping screenshots. But I get a v6 addresses on my mobile and it can browse to ipv6.google dot com. The device also passes v6 tests.

BSNL may not have rolled out v6 in your town fully and that's why you cannot use it.