Here @gautambhatia88 explains the phone tapping legal issues, but permit me to throw a little light on the implementation side as well.
Anyone who has ever worked with a telco knows "Lawful Interception" or "LI" is a horrific breach of rights. It works on whims of the govt https://twitter.com/gautambhatia88/status/1312285824424308736

LI capability is literally the only thing that can make the government not give you a go-ahead of service roll-out. Network quality, network reach, even pricing can be managed, but there's no compromise in LI. It is probably the most painfully QA-d part of the whole telco set-up.

Interception is built into the system, so cops / anyone else don't need to go through huge hassles to get your call / SMS records or content. Only a few people in the telco ever gets to know when an interception request comes in and fulfilled.

This industrial scale snooping operation means it is next to impossible to get the scale of snooping. It's not secret, it's just so vast and so many people are involved in it that it is practically impossible to know which phones are being snooped on by whom.

The process is also unbelievably opaque. The LI request may come from specific people, but they are under no obligation to disclose who the request originated from. I don't know if that's legal, that's just the way it works.

Finally, the telco is prohibited from disclosing LI requests. So even if the telco knows about an illegal spying operation against you, they cannot tell you (not that they would want to, obviously).

In summary, it's a complete travesty otlf justice and due process.

This is also why India is unlikely to ever get Skype / Google calling to phone numbers. "Lawful Interception" is the only problem.