You need I485 to apply EAD.

You have to apply I485 in order to apply EAD. I140 alone does not qualify you for a EAD. You can apply I140/I485 concurrently so you will get a EAD before I140 approval. Just like Immcanada said, if you use EAD, you will lost your non-immigration status. So better not to use it even if you get it.