Two Sequences on one column You can use 1 or 2 sequence.

Let's say I have a table tblOrder and 2 columns in it, OrderID and Company. I only use two companies in my table, IBM and Airtel.

What I want is when  Company = IBM then OrderID insert as 1 and when company is Airtel then it should insert OrderID as 1001 and repeat steps with increment 1, meaning next OrderID for IBM should be 2 and for Airtel should be 1002.

I think I need to use two sequences, on one column with case expression.
Create two sequences, one for IBM and one for Airtel. Set the start points appropriately. Put all the logic in a stored procedure. Pick the right one for each INSERT.

This is not a great design. Surrogate keys like this are best if they are completely meaningless. By tying a range of values to a customer you may have problems in the future. What will you do when a range is exhausted? What if you acquire another customer? Will you tolerate gaps in the sequence? For a short-lived, single-purpose application you may be OK. For an enterprise application it is a risk.