imessage: free with 3G?

Hello,

I have a quick question about imessages. I have already read a few posts saying imessage works with both wifi and 3G.

However, I just want to make sure a few things:

1. If it is working under 3G, is it still free or does it use my data plan?

2. If i am imessaging with someone who is not in the same country as me is imessaging through 3G still free?

Please let me know. Thank you!