Like noaim said, there is no way to check "count". iMessage uses data to send the messages, just like bbm on Blackberry does-if that helps you to understand it more.
Originally Posted by noaim
So when you iMessage, it goes towards your data usage. Now, I know some have the limited data plan, like 2gb, some have larger-one of my daughters is on the 2gig. While at home she's hooked to wifi, but during the day she's at school. I can honestly say as much as she does with fb, online, etc. She's only used just about a 1/4 of a gig only. We have 8 days left till our billing cycle closes, I'd be very surprised if in this 8 days her usage reachs the 1gig point, never mind the 2 she's allowed. Also, after speaking with a VzW rep the beginning of this month, iMessage barely uses any data, and when your on wifi, it doesn't goes towards your monthly data plan at all.