I'm confirming what Dan said. Blue text messaging bubbles means you are utilizing Apple's new iOS 5 feature, iMessaing, which means you are texting another person using an Apple mobile device with iOS 5 such as an iPad, iPod Touch, or iPhone
. These text messages are real and do not count toward your carrier bill. Green text messaging bubbles mean you are texting someone who is using a non apple device or they simply haven't upgraded to the latest iOS mobile software.