Quoting from the official site:
* Existing EVDO customers would continue to avail the unlimited data usage@Rs 650 per month
This means, all existing users can continue enjoying unlimited internet at Rs. 650 per month. However the asterisk sign in the very beginning of that sentence also says that it might be for a time being. And they might increase the unlimited tariff for existing customers as well.
To conclude, it will be good for both BSNL and as well as its existing customers as far the price for unlimited tariff remains the same. If they still have future ideas of hiking for their valuable existing customers, they will definitely lose some of their customers in very short period of time.
I would like to thank ashish_evdo for updating us with the news and dark_king for bringing this into my concern via his BSNL-EVDO-CLUB SMS Channel.