Thanks for your reply.  Do you have a source where I can confirm this?  I haven't seen any documentation that says that using the cellular network and not wifi will count against my data plan when receiving an iMessage.  Apple's website says:

"You can send unlimited text messages via Wi-Fi or 3G from your iPad, iPhone, or iPond touch to anyone with one of those devices"

Now that I read this again, it doesn't say anything about receiving these messages, does it?  And that was my original question.

I'm still confused about this issue.