As I said earlier, a Postpaid corporate connection from Airtel can be formed by a group of minimum 3 numbers, including the Data card number. Visit Airtel store for more info. Corp postpaid plans are much better than normal postpaid plans. In normal MyPlan, you get 400 minutes for Rs199 plan, whereas in Corporate MyPlan you get 600 minutes. Now coming to the point of getting the connection:-
As I said earlier, If you have a friend using Airtel Corp connection, then ask him to get a new data card connection for you with the above said plan -- This is the easiest one.
If you have 2 Airtel connections (either prepaid or normal postpaid or MNP from other operator) you can form new Corp connection with data card connection as third number and enjoy free unlimited calls within the 2 numbers as bonus.
Another suggestion.. Why don't you try Jio Preview offer? That is buying the LYF wind4 with Jio SIM and use it for tethering? Considering the price of phone / features + 3 months UL 4G data, its better than getting new corp connection from Airtel, if you are OK with current operator..