Can I still use iMessage if I don't have a plan?

I got my moms old iPhone 3, but I don't have a plan. Can I still use iMessage without a plan?

Definitely as long as iphone 3 can run a later OS (I know people with 3GS have imessage), so thats the question. I know people with ipads that imessage me all the time and they have no cell plan.

3G or 3GS. There's no iPhone 3.

You should be able to via Wi-Fi.