Till May 2008 I worked for my employer "A" at Client's location C. Then From June, I changed my employer to "B" but working for same client "C" --at same location---with same job position. I have two W2's. One from A and another one from B.
Can I file Itemized deduction or I need to do std deduction?

Whether you can itemize or not has nothing to do where your inconme came from. It depends on whether you have enough deductions to exceed the standard deduction.

You can itemize deductions if your itemized deductions are more than standard deduction.