Will iMessage use my prepaid credit?

I recently bought and iPhone 4s and just wanted to know. My girlfriend has an iPhone 4 and she activated iMessage and it chewed up all of her credit once she started using it after activation, any information would be helpful. I'm on Optus 2 dollar a day prepaid.

No imessage send free message between all apple device.

That's not at all possible.iMessage is a free messaging app n just uses your data credit. Probably your friend was using the application widout any data plan activated so it just deebited all the amount of data used from her credit charge…

Hope this helps