Does sending/receiving pictures and videos on iMessage cost data on AT&T?

Does sending/receiving pictures and videos on iMessage cost data on AT&T?

Added (1). I recent, y traded my iPod Touch 5 for and iPhone 5 and I will be using the same plan that I have had with my old phone; unlimited call and texting but the smallest amount of data possible. Will I be able to send pictures/videos off of Wi-Fi on iMessage without using up my data? And once I put a sim in it I can use my iPhone just like my iPod, right?

If doing so off of a Wi-Fi connection, yes. On any carrier.