Do you get charged to activate iMessage on your iPhone?

I want to use iMessage in order to contact other people that have an iPhone/iPod/iPad and I know that it's free provided you have an Internet connection, but when I went to turn it on, it says: "Your carrier may charge for SMS messages used to activate iMessage". What does this mean? What is it going to charge me for?

I think it just means that if you do not have Wi-Fi signal, you can re-send the message as an SMS, which would cost money. However, as long as you have Wi-Fi signal, you will not be charged.

It's free for you and anyone texting over Wi-Fi on an iPhone, iPad, iPod touch, or Mac with iMessage. So make sure its on Wi-Fi.

If your next question is

How can I tell if I'm sending an iMessage or an SMS text message?

Then here is the answer:
The "Send" button will be light blue when sending an iMessage as opposed to green for text messages.
The bubble that contains your sent message will also be blue again, as opposed to green for text messages

Hope this helps!

To activate imessage, apple automatically sends one international txt msg and if you don't have it in your plan it will b a one time additional charge of.20