How can i tell if iMessage is used, or it's been treated like a text message?
Your iMessage bubbles will be blue and the text bubbles will remain green. The replies from the other person will continue to be white but from now on they will appear in a block with the header Text Message or iMessage.
OK, so imesssage exists to use wifi to send your text when your cell service isnt available, right?
No, iMessage exists to send messages solely between iOS devices using Apple's messaging system and servers. Your SMS text message from your cell service provider is still in operation and will be used when iMessage cannot - that is when sent to a non-Apple iOS device with iMessage setup (although in iMessage settings you can disable the send as SMS option, in which case if the recepient is not using iOS and iMessage, the your message will fail).
iMessage will use wifi whenever it is available by preference, but when you are not connected to a wifi node, it will use cellular data (which will count against your plan) instead.
iMessage vs text
