iMessage on iPad: how do I know when the message is an sms or not? I've upgraded to iOS8. I have an iPad and an iPhone.

I'm chatting with a friend through his phone number with my iPad. I guess the iPad is using the iPhone carrier to send the sms. All works good.

Then I decided to turn off my iPhone and surprisingly the messages keep arriving to my friend. Without the carrier !?

I wonder, are they really sms? How can I check this on the ipad? They are all blue messages, and my friend number is highlighted in the contact profile (There is no email, just the number).
all blue messages are iMessages,
all green messages are sms text messages,

later this month you'll be able to use your ipad to send text messages from your iphone... as of now, all ipads use iMessage only!