Just like any other government service, MTNL has its flaws.
Starting with Speed: Speed provided by them is just too slow and half of what they promise.
Connectivity: Frequent disconnections and sometimes no Connectivity for hours.
Service: Hahaha. Just too pathetic and popular to write here. But still. They work at snail pace. It takes 15 days after requesting to get a new connection. And in case of speed or billing issues service provided by customer service is poor.
And in case there is a fault in telephone line. It will take like eternity for them to visit you and repair the line.